Composite positive electrode active material, positive electrode containing the same, and all-solid-state secondary battery

Abstract

The composite cathode active material comprises a composite of M2S, an alkali metal salt, and a carbon-based material, where M is an alkali metal, and the alkali metal is either Li or Na, and the size of the M2S crystallite obtained from the XRD spectrum of the composite is less than 9.9 nm, and the composite comprises a solid solution of M2S and an alkali metal salt. A composite cathode active material, a cathode containing the same, and an all-solid-state secondary battery are provided.

Description

[Technical Field]

[0001] This invention relates to a composite positive electrode active material, a positive electrode containing the same, and an all-solid-state secondary battery. [Background technology]

[0002] Recently, industrial demands have led to active development of batteries with high energy density and safety. For example, lithium batteries are used in a variety of applications, including information equipment, communication equipment, and automobiles. In the case of automobiles, safety is paramount because it involves human lives.

[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 rechargeable batteries using solid electrolytes instead of liquid electrolytes have been proposed. Solid electrolytes have a lower risk of ignition compared to liquid electrolytes.

[0004] All-solid-state rechargeable batteries can reduce the possibility of fire and explosion by using a solid electrolyte instead of a liquid electrolyte. All-solid-state batteries can offer improved safety. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The problem that this invention aims to solve is to provide a composite cathode active material that improves specific capacity and cycle characteristics by reducing crystallite size.

[0006] Furthermore, the problem that the present invention aims to solve is to provide a positive electrode containing the above-mentioned composite positive electrode active material.

[0007] Furthermore, the problem that the present invention aims to solve is to provide an all-solid-state secondary battery including the positive electrode described above. [Means for solving the problem]

[0008] In one embodiment, It contains a composite of M2S, alkali metal salts, and carbon-based materials. M is an alkali metal, and the alkali metal is either Li or Na. The size of the M2S crystallite obtained from the XRD spectrum of the composite is less than 9.9 nm. A composite cathode active material is provided, in which the composite contains a solid solution of M2S and an alkali metal salt.

[0009] In other embodiments, The positive electrode current collector and the positive electrode active material layer disposed on one or both sides of the positive electrode current collector are included. A positive electrode is provided in which the positive electrode active material layer comprises the above-mentioned composite positive electrode active material and a solid electrolyte (for example, a sulfide-based solid electrolyte).

[0010] In other embodiments, The device includes the positive electrode, the negative electrode, and an electrolyte layer disposed between the positive and negative electrodes as described above. An all-solid-state secondary battery is provided, which includes a negative electrode current collector and a first negative electrode active material layer disposed on one surface of the negative electrode current collector.

[0011] In other embodiments, The device includes the positive electrode, the negative electrode, and an electrolyte layer disposed between the positive and negative electrodes as described above. A solid-state secondary battery is provided in which the positive electrode contains the composite positive electrode active material described above. [Effects of the Invention]

[0012] In one embodiment, by providing a composite positive electrode active material with reduced crystallite size, an all-solid-state secondary battery can be provided with increased specific capacity and improved cycle characteristics. [Brief explanation of the drawing]

[0013] [Figure 1] These are the XRD spectra of pulverized Li2S, the Li2S-LiI complex which is an intermediate product of Example 1, and the Li2S-LiI-CNF complex prepared in Example 1. [Figure 2A] This is a scanning electron microscope image of the Li2S used in Example 1. [Figure 2B] This is a scanning electron microscope image of the Li2S-LiI-CNF composite fabricated in Example 1. [Figure 3] This is a cross-sectional view of an all-solid-state secondary battery in an exemplary embodiment. [Figure 4] This is a cross-sectional view of an all-solid-state secondary battery in an exemplary embodiment. [Figure 5] This is a cross-sectional view of an all-solid-state secondary battery in an exemplary embodiment. [Figure 6] This is a cross-sectional view of an all-solid-state secondary battery in an exemplary embodiment. [Figure 7] This is a cross-sectional view of an all-solid-state secondary battery in an exemplary embodiment. [Modes for carrying out the invention]

[0014] Unless otherwise specifically defined, all terms used in this invention (including technical and scientific terms) have the same meaning as those generally understood by a person of ordinary skill in the art to which this invention pertains. Furthermore, terms as defined in commonly used dictionaries should be interpreted to have the meaning consistent with their meaning in the relevant art and in the context of this disclosure, and should not be interpreted in an idealized or overly formal sense.

[0015] The present invention is described with reference to exemplary embodiments and cross-sectional views which are schematic diagrams of idealized embodiments. Thus, deformation from the illustrated shape must be expected as a result of, for example, manufacturing techniques and / or tolerances. Accordingly, embodiments described herein should not be construed as being limited to specific shapes of regions as illustrated herein, and should include, for example, deviations of shape caused by manufacturing. For example, a region illustrated or described as flat may typically be rough and / or have nonlinear features. Furthermore, corners that are sharply illustrated may also be rounded. Accordingly, regions illustrated in the drawings are essentially schematic, and their shapes are not intended to illustrate the exact shape of the region and are not intended to limit the scope of the claims.

[0016] The present technical concept can be embodied in various other forms and should not be construed as being limited to the embodiments described herein. The embodiments are provided to ensure that the present invention is thorough and complete, and to fully convey the scope of the present technical concept to those ordinary in the art. Same reference numerals refer to the same components.

[0017] When one component is said to be "on top of" another, one will understand that it is either directly above the other component or that the other component may be interposed between them. In contrast, when one component is said to be "directly on top of" another, there is no component interposed between them.

[0018] The terms "first," "second," "third," etc., may be used in the present invention to describe a variety of components, elements, regions, layers, and / or areas, but these components, elements, regions, layers, and / or areas should not be limited by these terms. These terms are used to distinguish one component, element, region, layer, or area from other elements, elements, regions, layers, or areas. Accordingly, the first component, element, region, layer, or area described below may be referred to as the second component, element, region, layer, or area without deviating from the teachings of the present invention.

[0019] The terminology used in this invention is for the purpose of describing specific embodiments only and is not intended to limit the technical idea. The singular form used herein includes plural forms, including “at least one,” unless the content expressly indicates otherwise. “At least one” should not be construed as limiting to the singular. The term “and / or” as used herein includes all any combination of one or more of the list items. The terms “including” and / or “including” as used in the detailed description specify the presence of expressed features, regions, integers, stages, operations, components, and / or ingredients, and do not exclude the presence or addition of one or more other features, regions, integers, stages, operations, components, ingredients, and / or groups thereof.

[0020] Spatially relative terms such as “down,” “underside,” “bottom,” “up,” “top,” and “upper” may be used here to easily describe the relationship between one component or feature and other components or features. Spatially relative terms, when used or operated in addition to the orientation illustrated in the drawings, will be understood to include different orientations of the apparatus. For example, if the apparatus in the drawing is inverted, a component described as “below” or “below” another component or feature will be oriented “above” the other component or feature. Thus, the exemplary term “down” may encompass both upward and downward. The apparatus may be positioned in other orientations (rotated 90° or in different directions), and the spatially relative terms used in this invention may be interpreted accordingly.

[0021] "Group" refers to a group of elements in the periodic table according to the International Union of Pure and Applied Chemistry ("IUPAC") classification system of groups 1-18.

[0022] In this invention, "particle size" refers to the average diameter when the particle is spherical, and to the average major axis length when the particle is non-spherical. The particle size can be measured using a particle size analyzer (PSA). "Particle size" is, for example, the average particle size. "Average particle size" is, for example, the median particle size, D50.

[0023] D50 is the particle size that corresponds to the 50% cumulative volume calculated from the smallest particle size in the particle size distribution measured by laser diffraction.

[0024] D90 is the particle size that corresponds to the 90% cumulative volume calculated from the smallest particle size in the particle size distribution measured by laser diffraction.

[0025] D10 is the particle size that corresponds to the 10% cumulative volume, calculated from the smallest particle size in the particle size distribution measured by laser diffraction.

[0026] In this invention, "metal" includes both metals and metalloids such as silicon and germanium, in either an elemental or ionic state.

[0027] In this invention, "alloy" means a mixture of two or more metals.

[0028] In this invention, "electrode active material" means an electrode material that can be lithium-treated and delithiated.

[0029] In this invention, "positive electrode active material" means a positive electrode material that can be lithium-ionized and delithiated.

[0030] In this invention, "negative electrode active material" means a negative electrode material that can be lithium-treated and delithiated.

[0031] In this invention, "lithification" and "lithification" refer to the process of adding lithium to the electrode active material.

[0032] In this invention, "desitization" and "to delithiate" refer to the process of removing lithium from the electrode active material.

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

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

[0035] In this invention, "positive electrode" and "cathode" refer to electrodes in which electrochemical reduction and lithiumization occur during the discharge process.

[0036] In this invention, "negative electrode" and "anode" refer to electrodes in which electrochemical oxidation and delithiation occur during the discharge process.

[0037] While specific embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are not currently anticipated or foreseeable may arise for the applicant or those skilled in the art. Accordingly, the filed and modifiable claims are intended to include all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0038] The following describes in more detail the composite positive electrode active material, the positive electrode containing the same, and the all-solid-state secondary battery in exemplary embodiments.

[0039] [Composite positive electrode active material] In one embodiment, the composite cathode active material includes a composite of M2S, an alkali metal salt, and a carbon-based material. M is an alkali metal. The alkali metal is Li or Na. M2S is, for example, Li2S or Na2S. The size of the M2S crystallite obtained from the XRD spectrum of the composite is less than 9.9 nm. The size of the M2S crystallite obtained from the XRD spectrum of the composite is, for example, 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 crystallite obtained from the XRD spectrum of the composite is, for example, 1 to less than 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 contains a solid solution of M2S and an alkali metal salt.

[0040] By forming a composite with alkali metal salts and carbon-based materials, the ionic and electronic conductivity of M2S can be simultaneously improved. The inclusion of alkali metal salts in the composite improves the ionic conductivity of the composite cathode active material, reducing the internal resistance of the cathode containing the composite cathode active material and the lithium battery. The inclusion of carbon-based materials in the composite improves the electronic conductivity of the composite cathode active material, further reducing the internal resistance of the cathode containing the composite cathode active material and the lithium battery.

[0041] The composite material contains M2S crystallites, and by reducing the size of the M2S crystallites to 21 nm or less, the volume change of the M2S crystallites during charging and discharging can be mitigated. For example, by reducing the size of the M2S crystallites, the volume change caused by a single M2S crystallite is reduced, thus mitigating the overall volume change of the composite material during charging and discharging. For example, by reducing the size of the M2S crystallites, the grain boundaries between multiple M2S crystallites can more easily accommodate the volume change of the M2S crystallites during charging and discharging, thus mitigating the volume change of the composite material during charging and discharging. This reduces the possibility of defects such as cracks occurring due to volume changes in the composite material during charging and discharging. By including such a composite in the composite cathode active material, the cycle characteristics of secondary batteries containing the composite cathode active material can be improved. For example, the life characteristics of lithium batteries containing such a composite cathode active material are improved.

[0042] The composite contains 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. This increased contact area between the M2S crystallites and the alkali metal salt and / or carbon-based material can further improve the ionic conductivity and / or battery conductivity of the composite. The inclusion of such a composite in the composite cathode active material can improve the reversibility of the electrode reaction in a secondary battery containing the composite cathode active material. As a result, the specific capacity of the composite cathode active material can be increased.

[0043] The ionic conductivity of a 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 contains alkali metal ions arranged within the M2S crystallite, the ionic conductivity of the solid solution of M2S and an alkali metal salt can be improved compared to the ionic conductivity of M2S alone. As a result, the ionic conductivity of the composite can be improved, and the internal resistance of the composite can be reduced. The inclusion of such a composite cathode active material can improve the cycle characteristics of a secondary battery containing the composite cathode active material. For example, the high-efficiency characteristics of a secondary battery containing such a composite cathode active material can be improved.

[0044] Li2S-alkali metal salt-carbon material composites are distinguished from simple mixtures of Li2S, alkali metal salts, and carbon materials. Simple mixtures of Li2S, alkali metal salts, and carbon materials fail to maintain a dense interface between them, resulting in high interfacial resistance, which can consequently reduce the lifespan characteristics of secondary batteries.

[0045] The composite contains M2S. Since M2S has a high theoretical capacity, it can provide a secondary battery with a high energy density. However, because M2S has low ionic and / or electronic conductivity, a composite is formed with alkali metal salts and carbon-based materials to overcome this disadvantage. The M2S content in the composite can be, for example, 10-80 wt%, 20-70 wt%, 30-60 wt%, or 40-60 wt% of the total weight of the composite. If the M2S content is excessively high, improving the ionic and / or electronic conductivity of M2S is not easy. If the M2S content is excessively low, the energy density of the secondary battery may decrease.

[0046] The complex contains alkali metal salts. Alkali metal salts are, for example, compounds that do not contain sulfur (S). Alkali metal salts can also be, for example, binary compounds or ternary compounds. Alkali metal salts can also be binary compounds consisting of, for example, an alkali metal and one element selected from groups 13 to 17 of the periodic table. Alkali metal salts can also be ternary compounds consisting of, for example, an alkali metal and two elements selected from groups 13 to 17 of the periodic table.

[0047] Alkali metal salts are, for example, lithium salts. Lithium salt binary compounds may include, for example, LiI, LiBr, LiCl, LiF, LiH, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, LiB3, or combinations thereof. Lithium salt ternary compounds may include, for example, Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, Li3BN2, or combinations thereof. The inclusion of such lithium salts in the complex can further improve its ionic conductivity. Such lithium salts can, for example, more readily form solid solutions with Li2S within the complex.

[0048] Alkali metal salts are, for example, sodium salts. Sodium salt binary compounds may include, for example, NaI, NaBr, NaCl, NaF, Na2O, Na2Se, Na3N, Na3P, Na3As, Na3Sb, Na3Al2, NaB3, or combinations thereof. Sodium salt ternary compounds may include, for example, Na3OCl, NaBF4, NaPF6, NaAsF6, NaClO4, NaNO3, NaAlO2, NaAlCl4, NaNO3, Na2CO3, NaBH4, Na2SO4, Na3BO3, Na3PO4, Na4NCl, Na5NCl2, Na3BN2, or combinations thereof. The inclusion of such sodium salts in the complex can further improve the ionic conductivity of the complex. Such sodium salts can, for example, more readily form solid solutions with Na2S within the complex.

[0049] The alkali metal salt content in the composite can be 1-40 wt%, 5-35 wt%, 10-35 wt%, 15-35 wt%, 20-35 wt%, or 25-35 wt% of the total weight of the composite. If the alkali metal salt content is excessively high (for example, excessively high), the energy density of the secondary battery may decrease. If the alkali metal salt content is excessively low, the ionic conductivity of the composite may decrease, increasing the internal resistance of the composite cathode active material. As a result, the cycle characteristics of the secondary battery may deteriorate.

[0050] In the composite, the molar ratio of M2S to alkali metal salt can be, for example, 50:50-95:5, 60:40-95:5, 60:40-90:10, 65:35-90:10, 65:35-85:15, or 70:30-85:15. The molar ratio of M2S to alkali metal salt in the composite can also be, for example, 50:50-95:5, 50:50-90:10, 50:50-85:15, 50:50-80:20, 50:50-75:25, or 50:50-70:30. Having M2S and alkali metal salt in such a range of molar ratios can further improve the cycle characteristics of secondary batteries containing the composite cathode active material. However, if the molar ratio of M2S is excessively high, the effect of the alkali metal salt on improving ionic conductivity will be minimal. If the molar ratio of M2S is excessively low, the energy density of a secondary battery containing a composite cathode active material may decrease.

[0051] In composites, the molar ratio of Li2S to lithium salt can be, for example, 50:50-95:5, 60:40-95:5, 60:40-90:10, 65:35-90:10, 65:35-85:15, or 70:30-85:15. The molar ratio of Li2S to lithium salt in composites can also be, for example, 50:50-95:5, 50:50-90:10, 50:50-85:15, 50:50-80:20, 50:50-75:25, or 50:50-70:30. Having Li2S and lithium salt in such a range of molar ratios can further improve the cycle characteristics of lithium batteries containing composite cathode active materials. However, if the molar ratio of Li2S is excessively high, the ionic conductivity improvement effect of the lithium salt will be minimal. If the molar ratio of Li2S is excessively low, the energy density of lithium batteries containing composite cathode active materials may decrease.

[0052] In the composite, the molar ratio of Na2S to sodium salt can be, for example, 50:50-95:5, 60:40-95:5, 60:40-90:10, 65:35-90:10, 65:35-85:15, or 70:30-85:15. The molar ratio of Na2S to sodium salt in the composite can also be, for example, 50:50-95:5, 50:50-90:10, 50:50-85:15, 50:50-80:20, 50:50-75:25, or 50:50-70:30. Having a molar ratio of Na2S to sodium salt within this range can further improve the cycle characteristics of sodium batteries containing the composite cathode active material. However, if the molar ratio of Na2S is excessively high, the effect of the sodium salt on improving ionic conductivity will be minimal. If the molar ratio of Na2S is excessively high, the energy density of a sodium battery containing a composite cathode active material may decrease.

[0053] The composite includes a carbon-based material. The carbon-based material can be any material containing carbon atoms that is used as a conductive material in the art. The carbon-based material may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The carbon-based material may be, for example, a calcined product of a carbon precursor. The carbon-based material may be, for example, a carbon nanostructure. The carbon nanostructure may 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 may be, for example, a carbon nanotube (CNT), a carbon nanofiber (CNF), a carbon nanobelt, a carbon nanorod, graphene, or a combination thereof. The carbon-based material may be, for example, a porous carbon-based material or a non-porous carbon-based material. The porous carbon-based material may, for example, include periodic and regular two-dimensional or three-dimensional pores. Porous carbon-based materials can be, for example, carbon black such as Ketjenblack, acetylene black, Denka black, thermal black, and channel black, graphite, activated carbon, or combinations thereof. The form of carbon-based materials can be, for example, particulate, sheet, or flake, but is not limited to these; any form used as a carbon-based material in the relevant art is acceptable.

[0054] The carbon-based material content in the composite can be, for example, 1-20 wt%, 5-20 wt%, or 10-20 wt% of the total weight of the composite. If the carbon-based material content increases excessively, the energy density of the secondary battery may decrease. If the carbon-based material content decreases excessively, the electronic conductivity of the composite may decrease, and the internal resistance of the composite cathode active material may increase. As a result, the cycle characteristics of the secondary battery may deteriorate.

[0055] In the XRD spectrum of the composite, for example, the first lattice constant d1 derived from the first peak at a diffraction angle 2θ = 27° ± 2.0° corresponding to the 111 crystal plane of M2S can be even larger than the second lattice constant d2 derived from the second peak at a diffraction angle 2θ = 27° ± 2.0° corresponding to the 111 crystal plane of M2S in the XRD spectrum of M2S used to manufacture the composite. Because the M2S-alkali metal salt-carbon material composite has a larger lattice constant d than the M2S used to manufacture the composite, alkali metal ions can be transferred more easily within the M2S crystal structure of the composite. Therefore, the ionic conductivity of the composite cathode active material containing the composite can be further improved. The internal resistance of a secondary battery containing the composite cathode active material can be reduced, improving its cycle characteristics. The difference between the first lattice constant d1 and the second lattice constant d2 can be 0.05 Å or greater, 0.1 Å or greater, 0.15 Å or greater, 0.2 Å or greater, or 0.25 Å or greater. The magnitude of the first lattice constant d1 can be, for example, 5.78 Å or greater, 5.80 Å or greater, 5.82 Å or greater, 5.85 Å or greater, 5.90 Å or greater, 5.95 Å or greater, or 6.0 Å or greater. Having such a magnitude of first lattice constant d1 in the composite can further improve the ionic conductivity of the composite cathode active material containing the composite. This can reduce the internal resistance of a secondary battery containing the composite cathode active material, thereby improving its cycle characteristics.

[0056] In the XRD spectrum of the composite, for example, the first peak, indicated by a diffraction angle 2θ = 27° ± 2.0° corresponding to the 111 crystal plane of M2S, has the first diffraction angle, and the second peak, indicated by a diffraction angle 2θ = 27° ± 2.0° corresponding to the 111 crystal plane of M2S in the XRD spectrum of M2S used to manufacture the composite, has the second diffraction angle, with the first diffraction angle being smaller than the second diffraction angle. For example, the position of the first peak may shift to a lower angle compared to the position of the second peak. Therefore, the crystallite size of the M2S-alkali metal salt-carbon material composite can be reduced compared to the M2S used to manufacture the composite. By reducing the crystallite size of the M2S-alkali metal salt-carbon material composite, the volume change of crystallites during charging and discharging is reduced, thus mitigating the volume change during charging and discharging of composites containing multiple crystallites. This can suppress the occurrence of defects such as cracks during charging and discharging of composite cathode active materials containing such composites. As a result, the cycle characteristics of secondary batteries containing composite cathode active materials can be improved.

[0057] In the XRD spectrum of the composite, for example, the first peak indicated at a diffraction angle 2θ = 27° ± 2.0° corresponding to the 111 crystal plane of M2S has the first full width at half maximum (FWHM1), and in the XRD spectrum of M2S used to manufacture the composite, the second peak indicated at a diffraction angle 2θ = 27° ± 2.0° corresponding to the 111 crystal plane of M2S has the second full width at half maximum (FWHM2), and the first full width at half maximum may be even larger than the second full width at half maximum. Therefore, the M2S-alkali metal salt-carbon material composite can have increased lattice strain compared to the M2S used to manufacture the composite. For example, the M2S-alkali metal salt-carbon material composite can have increased lattice strain by forming a solid solution between M2S and the alkali metal salt. By having an increased full width at half maximum (FWHM) compared to the M2S used to manufacture the composite, the ionic conductivity of the composite cathode active material containing the composite can be further improved. The internal resistance of a secondary battery containing a composite positive electrode active material can be reduced, thereby improving its cycle characteristics.

[0058] The first half-width (FWHM) can be, for example, 1° or more, 1.05° or more, 1.10° or more, or 1.15° or more. Having a first FWHM1 within such a range of the composite material further improves the ionic conductivity of the composite cathode active material containing the composite. This reduces the internal resistance of the secondary battery containing the composite cathode active material, improving its cycle characteristics.

[0059] The Mohs hardness of alkali metal salts and carbon-based materials may be even greater than that of M2S. For example, the Mohs hardness of M2S is 0.6 or less. For example, the Mohs hardness of Li2S is 0.6.

[0060] The Mohs hardness of the alkali metal salt can be 0.7 or higher, 0.8 or higher, 0.9 or higher, 1.0 or higher, 1.5 or higher, or 2.0 or higher. Having such a range of Mohs hardness in the alkali metal salt makes it easier to grind M2S during the milling process and to form a solid solution of M2S and the alkali metal salt more easily. For example, the Mohs hardness of LiI is 2.0. For example, the Mohs hardness of NaI is 2.1.

[0061] The Mohs hardness of the carbon-based materials can be 0.7 or higher, 0.8 or higher, 0.9 or higher, 1.0 or higher, 1.2 or higher, or 1.5 or higher, respectively. Having such a range of Mohs hardness in the carbon-based materials facilitates the grinding of M2S during the milling process and facilitates the formation of M2S-alkali metal salt-carbon-based material composites. For example, the mohs hardness of carbon nanofiber (CNF) is 1.5.

[0062] The composite cathode active material may have a particulate form. The particle size of the composite cathode active material, i.e., the size of the composite particles, may be, for example, 10 μm or less, 5 μm or less, 2 μm or less, 1.5 μm or less, or 1 μm or less. The size of the composite particles may be, for example, 0.1 to 10 μm, 0.1 to 5 μm, 0.1 to 2 μm, 0.1 to 1.5 μm, or 0.1 to 1 μm or less. By having the composite particles within such a size range, the volume change during charging and discharging is suppressed or reduced, thereby suppressing the degradation of the composite cathode active material containing the composite during charging and discharging. If the size of the composite particles increases excessively, the volume change of the composite during charging and discharging increases, which can accelerate the degradation of the composite cathode active material containing the composite. As a result, the cycle characteristics of a secondary battery containing such a composite cathode active material may deteriorate.

[0063] The size of M2S particles contained in the composite positive electrode active material can be, for example, 2 μm or less, 1.5 μm or less, or 1 μm or less. The size of the M2S particles can be, for example, 0.1 to 2 μm, 0.1 to 1.5 μm, or 0.1 to 1 μm or less. By having M2S particles within this size range, volume changes during charging and discharging are suppressed, which can suppress the degradation of the composite positive electrode active material containing the composite during charging and discharging. If the size of the M2S particles increases excessively, the volume change of the composite during charging and discharging increases, which can accelerate the degradation of the composite positive electrode active material containing the composite. As a result, the cycle characteristics of secondary batteries containing such composite positive electrode active materials may deteriorate.

[0064] Therefore, the cycle characteristics, such as the lifespan, of secondary batteries containing composite positive electrode active materials can be improved. The size of the composite particles, for example, the particle size of the composite, can be measured using, for example, a laser diffraction beam, a scanning electron microscope, etc. The particle size of the composite is, for example, the arithmetic mean of the particle sizes of multiple particles measured using software on a scanning electron microscope image.

[0065] The composite material includes a carbon-based material, which may include, for example, a fibrous carbon-based material. The inclusion of a fibrous carbon-based material in the composite material can further improve its electronic conductivity. The inclusion of a fibrous carbon-based material in the composite material can also facilitate electron conduction from the surface to the interior of the composite material. The internal resistance of the composite cathode active material containing the composite material is reduced, further improving the cycle characteristics of the secondary battery containing the composite cathode active material.

[0066] The aspect ratio of fibrous carbon-based materials 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 fibrous carbon-based materials can be, for example, 2-30, 3-30, 4-30, 5-30, 10-30, or 20-30. The aspect ratio of fibrous carbon-based materials can be, for example, 2-30, 2-20, 2-10, 2-8, 2-5, or 2-4. Having aspect ratios within such ranges improves the overall electronic conductivity of the composite and further mitigates localized imbalances in electronic conductivity within the composite. The aspect ratio of fibrous carbon-based materials, for example, the ratio of diameter to length of the fibrous carbon-based material, can be determined, for example, from scanning electron microscope (SEM) images.

[0067] Fibrous carbon-based materials may include, for example, carbon nanostructures. Carbon nanostructures may include, for example, carbon nanofibers (CNF), carbon nanotubes (CNT), carbon nanobelts, carbon nanorods, or combinations thereof.

[0068] Carbon nanostructures can form primary carbon nanostructures consisting of a single carbon nanostructure and secondary carbon nanostructures formed by the aggregation of multiple carbon nanostructures.

[0069] 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.

[0070] Secondary carbon nanostructures are structures formed, for example, by assembling primary carbon nanostructures so that they form bundles or ropes, either entirely or partially. Secondary carbon nanostructures may include, for example, bundle-type carbon nanostructures, rope-type carbon nanostructures, or combinations thereof. The diameter of secondary carbon nanostructures may be, for example, 2nm-200nm, 3nm-150nm, 5nm-100nm, 5nm-50nm, 5nm-30nm, or 5nm-20nm. The length of secondary carbon nanostructures may be, for example, 20nm-2μm, 30nm-1.5μm, 50nm-1μm, 50nm-500nm, 50nm-400nm, 50nm-300nm, 50nm-200nm, or 50nm-100nm. The diameter and length of secondary carbon nanostructures can be measured from scanning electron microscope (SEM) images or optical microscopes. On the other hand, the diameter and / or length of the secondary carbon nanostructures can be measured by laser diffraction. The secondary carbon nanostructures can be used in composite fabrication after being converted into primary carbon nanostructures by, for example, dispersion in a solvent.

[0071] For 100 parts by weight of the composite, it 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. 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 with respect to 100 parts by weight of the composite. The alkali metal salt content contained in the composite is, 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 with respect to 100 parts by weight of the composite. The content of the carbon-based material contained in the composite is, 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 with respect to 100 parts by weight of the composite. By having such ranges of M2S, alkali metal salt, and carbon-based material compositions in the composite, the composite positive electrode active material containing the composite can provide excellent ionic conductivity and / or electronic conductivity.

[0072] The ionic conductivity of the composite is, for example, 1×10 -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 S / cm or more at 25 °C. The ionic conductivity can be measured, for example, using electrochemical impedance spectroscopy, DC polarization method, etc. By having such a range of ionic conductivity in the composite, the internal resistance of the composite positive electrode active material containing the composite can be reduced. The cycle characteristics of the secondary battery containing the composite positive electrode active material can be improved. The electronic conductivity of the composite is, for example, 1×10 -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 -4The conductivity can be greater than or equal to S / cm. Electronic conductivity can be measured using methods such as impedance spectroscopy or DC polarization. Having such a range of electronic conductivity in the composite reduces the internal resistance of the composite cathode active material containing the composite. This improves the cycle characteristics of secondary batteries containing the composite cathode active material.

[0073] [Positive electrode] [Positive electrode: Positive electrode active material] In one embodiment, the 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 positive electrode active material layer includes the composite positive electrode active material and a solid electrolyte. The positive electrode may have a further reduced internal resistance due to the inclusion of the composite positive electrode active material and the solid electrolyte. Therefore, the cycle characteristics of a secondary battery equipped with a positive electrode can be further improved.

[0074] Referring to Figures 3 to 7, 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 solid electrolyte described above.

[0075] The positive electrode active material layer 12 may contain 40-90 parts by weight, 40-80 parts by weight, 50-80 parts by weight, or 50-70 parts by weight of composite positive electrode active material per 100 parts by weight. If the content of composite positive electrode active material decreases excessively, the energy density of the secondary battery will decrease. If the content of composite positive electrode active material increases excessively, the deterioration of the positive electrode may be accelerated due to volume changes in the positive electrode during charging and discharging. As a result, the cycle characteristics of the all-solid-state secondary battery 1 may deteriorate.

[0076] The positive electrode active material layer 12 may further contain other positive electrode active materials in addition to the composite positive electrode active material described above.

[0077] Other positive electrode active materials may include, for example, Li2S-containing composites. Li2S composites include, for example, composites of Li2S and carbon-based materials, composites of Li2S, carbon-based materials and solid electrolytes, composites of Li2S and solid electrolytes, composites of Li2S and lithium salts, composites of Li2S and metal carbides, composites of Li2S, carbon-based materials and metal carbides, composites of Li2S and metal nitrides, composites of Li2S, carbon-based materials and metal nitrides, or combinations thereof.

[0078] The composite of Li2S and 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 manufacturing method of the Li2S and carbon-based material composite may be a dry method, a wet method, or a combination thereof, but is not limited to these; any method used in the art is acceptable. Examples of manufacturing methods for the Li2S and carbon-based material composite include milling, heat treatment, and vapor deposition, but is not necessarily limited to these; any method used in the art is acceptable.

[0079] 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 Li2S and carbon-based material composite described above. The solid electrolyte can be any material used as an ion-conducting material in the art, for example. The solid electrolyte is, for example, an inorganic 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, or a combination thereof. A sulfide-based solid electrolyte contains, for example, Li, S, and P, and may further selectively contain halogen elements. The sulfide-based solid electrolyte can be selected from among the sulfide-based solid electrolytes used in the electrolyte layer. A sulfide-based solid electrolyte has a capacity of, for example, 1 × 10⁻⁶ at room temperature. -5 It can have an ionic conductivity of S / cm or higher. The oxide-based solid electrolyte contains, for example, Li, O, and transition metal elements, and may further selectively contain other elements. The oxide-based solid electrolyte has a conductivity of, for example, 1 × 10⁻¹⁶ at room temperature. -5The solid electrolyte may have an ionic conductivity of S / cm or higher. The oxide-based solid electrolyte can be selected from among the oxide-based solid electrolytes used in the electrolyte layer.

[0080] The Li2S and solid electrolyte composite includes a solid electrolyte. The term "solid electrolyte" refers to the Li2S and carbon-based material and solid electrolyte composite described above.

[0081] A Li2S-lithium salt composite 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 one or more lithium halide compounds selected from LiF, LiCl, LiBr, and LiI in particular. A Li2S-lithium salt composite can, for example, be a Li2S-lithium halide composite. The inclusion of a lithium halide compound in the Li2S-lithium salt composite can provide further improved ionic conductivity. A Li2S-lithium salt composite is distinguished from a simple mixture of Li2S, a carbon-based material, and a lithium salt. A simple mixture of Li2S and a lithium salt fails to maintain a dense interface between the Li2S and the lithium salt, resulting in high interfacial resistance and consequently reducing the lifetime characteristics of the all-solid-state secondary battery.

[0082] The Li2S-metal carbide composite contains a metal carbide. The metal carbide is, for example, a two-dimensional metal carbide. The two-dimensional metal carbide is, for example, M n+1 C n T x It is represented as (where M is a transition metal, T is a terminal group, T is O, OH and / or F, n=1, 2, or 3, and x is the number of terminal groups). A two-dimensional metal carbide is, for example, Ti2CT. x , (Ti 0.5 Nb 0.5 )2CT x Nb2CT x V2CT x Ti3C2T x , (V 0.5 , Cr 0.5 )3C2T x Ti3CNT x Ta4C3T xNb4C3T x Or a combination of these. The surface of the two-dimensional metal carbide is terminated with O, OH and / or F.

[0083] The composite of Li2S, carbon-based material, and metal carbide includes the carbon-based material and the metal carbide. The carbon-based material refers to the composite of Li2S and carbon-based material described above. The metal carbide refers to the composite of Li2S and metal carbide described above.

[0084] The Li2S and metal nitride composite contains a metal nitride. The metal nitride is, for example, a two-dimensional metal nitride. The two-dimensional metal nitride is, for example, M n+1 N n T x It is expressed as (where M is 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). The surface of the two-dimensional metal nitride is terminated with O, OH and / or F.

[0085] The composite of Li2S, carbon-based material, and metal nitride includes the carbon-based material and the metal nitride. The carbon-based material refers to the composite of Li2S and carbon-based material described above. The metal nitride refers to the composite of Li2S and metal nitride described above.

[0086] The positive electrode active material layer 12 may further contain, for example, a sulfide-based compound distinct from the positive electrode active material described above. The sulfide-based compound may be, for example, a compound containing a metal element other than Li and a sulfur element. The sulfide-based compound may be, for example, a compound containing a metal element belonging to Group 1 to 14 of the periodic table with an atomic weight of 10 or more and a sulfur element. The sulfide-based compound may be, for example, FeS2, VS2, NaS, MnS, FeS, NiS, CuS, or a combination thereof. The inclusion of a sulfide-based compound in the positive electrode active material layer 12 can further improve the cycle characteristics of the all-solid-state secondary battery 1. The content of such sulfide-based compounds in the positive electrode active material layer 12 may be 10 wt% or less, 5 wt% or less, 3 wt% or less, or 1 wt% or less of the total weight of the positive electrode active material layer 12.

[0087] [Positive electrode: Solid electrolyte] The positive electrode active material layer 12 may further contain, for example, a solid electrolyte. The solid electrolyte may be, for example, a sulfide-based solid electrolyte. The solid electrolyte contained in the positive electrode 10 may be the same as or different from the solid electrolyte contained in the electrolyte layer 30. For detailed information on the solid electrolyte, refer to the section on the electrolyte layer 30.

[0088] The solid electrolyte contained in the positive electrode active material layer 12 has a smaller D50 average particle size than the solid electrolyte contained in the electrolyte layer 30. For example, the D50 average particle size of the solid electrolyte contained 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 D50 average particle size of the solid electrolyte contained in the electrolyte layer 30. The D50 average particle size is, for example, the median particle size (D50). The median particle size (D50) is, for example, the particle size corresponding to the 50% cumulative volume calculated from the particle size with the smallest particle size in the particle size distribution measured by laser diffraction.

[0089] The positive electrode active material layer 12 may contain 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 of solid electrolyte per 100 parts by weight. If the content of the solid electrolyte is excessively reduced, the internal resistance of the positive electrode 10 may increase, which may degrade the cycle characteristics of the all-solid-state secondary battery 1. If the content of the sulfide-based solid electrolyte is excessively increased, the energy density of the all-solid-state secondary battery 1 may decrease.

[0090] [Positive electrode: conductive material] The positive electrode active material layer 12 may further contain a conductive material. The conductive material may be, for example, a carbon-based conductive material, a metallic conductive material, or a combination thereof. The carbon-based conductive material may be, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or a combination thereof, but is not limited to these; any material used as a carbon-based conductive material in the art may be used. The metallic conductive material may be, for example, metal powder, metal fiber, or a combination thereof; any material used as a metallic conductive material in the art may be used. The conductive material content in the positive electrode active material layer 12 may be, for example, 1 wt% to 30 wt%, 1 wt% to 20 wt%, or 1 wt% to 10 wt% of the total weight of the positive electrode active material layer 12.

[0091] The positive electrode active material layer 12 contains a carbon-based material, and the carbon-based material may be present only in the composite positive electrode active material. The positive electrode active material layer 12 does not contain any other carbon-based material in addition to the composite positive electrode active material containing the carbon-based material. By not including any other carbon-based material in the positive electrode active material layer, the energy density of the positive electrode 10 and the all-solid-state secondary battery 1 can be improved and the manufacturing process can be simplified.

[0092] [Positive electrode: Binder] The positive electrode active material layer 12 may further contain a binder. The binder may be, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited to these; any binder usable in the art may be used. The binder content 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 is optional.

[0093] [Positive electrode: Other additives] In addition to the positive electrode active material, solid electrolyte, binder, and conductive material described above, the positive electrode active material layer 12 may further contain additives such as fillers, coating agents, dispersants, and ion conductivity enhancers.

[0094] The positive electrode active material layer 12 may contain fillers, coating agents, dispersants, ion conductivity enhancers, etc., and other known materials generally used in electrodes for all-solid-state secondary batteries can be used.

[0095] [Positive electrode: Positive electrode current collector] The positive electrode current collector 11 may be a plate or foil made of, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof. The positive electrode current collector 11 is optional. The thickness of the positive electrode current collector 11 may be, for example, 1 μm to 100 μm, 1 μm to 50 μm, 5 μm to 25 μm, or 10 μm to 20 μm.

[0096] The positive electrode current collector 11 may include, for example, a base film and a metal layer disposed on one or both sides of the base film. The base film may include, for example, a polymer. The polymer may 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. By including an insulating thermoplastic polymer in the base film, the base film can soften or liquefy when a short circuit occurs, interrupting battery operation and suppressing a rapid increase in current. The metal layer may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), or alloys thereof. The metal layer can act as an electrochemical fuse, cutting off in the event of overcurrent to perform a short-circuit prevention function. The limit current and maximum current can be adjusted by adjusting the thickness of the metal layer. The metal layer can be electrodeposited or deposited onto the base film. Reducing the thickness of the metal layer reduces the limit current and / or maximum current of the positive electrode current collector 11, thereby improving the stability of the lithium battery during a short circuit. Lead tabs can be added to the metal layer for external connection. Lead tabs can be welded to the metal layer or the metal layer / base film laminate by ultrasonic welding, laser welding, spot welding, etc. During welding, the base film and / or metal layer melt, while the metal layer is electrically connected to the lead tab. To further strengthen the weld between the metal layer and the lead tab, a metal chip can be added between the metal layer and the lead tab. The metal chip can be a thin piece of the same material as the metal layer. The metal chip can be, for example, metal foil or metal mesh. The metal pieces could be, for example, aluminum foil, copper foil, or SUS (stainless steel) foil.After placing a metal chip on a metal layer, the lead tab can be welded to a metal chip / metal layer laminate or a metal chip / metal layer / base film laminate by welding the lead tab to the metal chip. During welding, the base film, metal layer, and / or metal chip melt, while the metal layer or metal layer / metal chip laminate can be electrically connected to the lead tab. A metal chip and / or lead tab may be added to a portion of the metal layer. The thickness of the base film can be, for example, 1-50 μm, 1.5-50 μm, 1.5-40 μm, or 1-30 μm. Having the base film in such a thickness range can further effectively reduce the weight of the electrode assembly. The melting point of the base film can be, for example, 100-300°C, 100-250°C or less, or 100-200°C. Having the base film in such a melting point range allows the base film to melt during the lead tab welding process, making it easy to bond to the lead tab. Surface treatments such as corona treatment can be performed on the base film to improve the adhesion between the base film and the metal layer. The thickness of the metal layer can be, for example, 0.01 to 3 μm, 0.1 to 3 μm, 0.1 to 2 μm, or 0.1 to 1 μm. Having the metal layer in such a thickness range ensures the stability of the electrode assembly while maintaining conductivity. The thickness of the metal piece can be, for example, 2 to 10 μm, 2 to 7 μm, or 4 to 6 μm. Having the metal piece in such a thickness range makes it easier to connect the metal layer and the lead tab. Having such a structure in the positive electrode current collector 11 reduces the weight of the positive electrode 10, and as a result, the energy density of the positive electrode 10 and the lithium battery can be improved.

[0097] [Positive electrode: Inert material] Referring to Figures 6 and 7, the positive electrode 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12 disposed on one surface of the positive electrode current collector. An inactive member 40 is disposed on one side surface of the positive electrode 10. Referring to Figure 6, the inactive member 40 is disposed on one side surface of the positive electrode active material layer 12 and the positive electrode current collector 11. Referring to Figure 7, the inactive member 40 is disposed on one side surface of the positive electrode active material layer 12 and is positioned between the electrolyte layer 30 and the positive electrode current collector 11 facing the electrolyte layer 30. The inactive member 40 is not disposed on one side surface of the positive electrode current collector 11. The electrolyte layer 30 may be, for example, a solid electrolyte layer.

[0098] The inclusion of the inert member 40 prevents cracking of the electrolyte layer 30 during the manufacturing and / or charging / discharging of the all-solid-state secondary battery 1, thereby improving the cycle characteristics of the all-solid-state secondary battery 1. In an all-solid-state secondary battery 1 without the inert member 40, uneven pressure is applied to the electrolyte layer 30 in contact with the positive electrode 10 during the manufacturing and / or charging / discharging of the all-solid-state secondary battery 1, causing cracks to occur in the electrolyte layer 30, and the growth of lithium metal through these cracks increases the likelihood of short circuits.

[0099] In the all-solid-state secondary battery 1, the thickness of the inert member 40 is either greater than or equal to the thickness of the positive electrode active material layer 12. On the other hand, in the all-solid-state secondary battery 1, the thickness of the inert member 40 is substantially the same as the thickness of the positive electrode 10. Because the thickness of the inert member 40 is the same as 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 in close contact, thereby reducing the interfacial resistance between the positive electrode 10 and the electrolyte layer 30. Furthermore, the electrolyte layer 30 is sufficiently sintered during the pressurized manufacturing process of the all-solid-state secondary battery 1, which reduces the internal resistance of the electrolyte layer 30 and the all-solid-state secondary battery 1 containing it.

[0100] The inert member 40 surrounds the side surface of the positive electrode 10 and contacts the electrolyte layer 30. By surrounding the side surface of the positive electrode 10 and contacting the electrolyte layer 30, the inert member 40 effectively suppresses cracks in the electrolyte layer 30 caused by the pressure difference during the pressurization process in the electrolyte layer 30 that does not come into contact with the positive electrode 20. The inert member 40 surrounds the side surface of the positive electrode 10 and separates it from the negative electrode 20, specifically the first negative electrode active material layer 22. The inert member 40 surrounds the side surface of the positive electrode 10 and contacts the electrolyte layer 30, separating it 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 due to lithium overcharging, is suppressed. For example, by placing the inert member 40 on one side surface of the positive electrode active material layer 12 and simultaneously on one side surface 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 can be further effectively suppressed.

[0101] Referring to Figures 6 and 7, 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 that occur 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, and 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 come into contact with the negative electrode 20. The inert member 40 fills, for example, the space that extends from one side of the positive electrode 30 to the end of the electrolyte layer 30.

[0102] Referring to Figures 6 and 7, 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, 1-30%, 1-25%, 1-20%, 1-15%, 1-10%, or 1-5% of the width between one side of the positive electrode 10 and the other side facing that side. If the width of the inert member 40 is excessively large, the energy density of the all-solid-state secondary battery 1 will decrease. If the width of the inert member 40 is excessively small, the effect of placing the inert member 40 will be negligible.

[0103] The area of ​​the positive electrode 10 is smaller than the area of ​​the electrolyte layer 30 that is in contact with the positive electrode 10. The inert member 40 is positioned around the sides of the positive electrode 10 to compensate for the area difference between the positive electrode 10 and the electrolyte layer 30. By compensating for the difference between the area of ​​the positive electrode 10 and the area of ​​the electrolyte layer 30 with the area of ​​the inert member 40, 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 positive electrode 10 and the area of ​​the inert member 40 is the same as the area of ​​the electrolyte layer 30. The electrolyte layer 30 may be, for example, a solid electrolyte layer.

[0104] The area 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 of ​​the electrolyte layer 30. The area 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 of ​​the electrolyte layer 30.

[0105] If the area of ​​the positive electrode 10 is the same as or larger than the area of ​​the electrolyte layer 30, a short circuit may occur due to physical contact between the positive electrode 10 and the first negative electrode active material layer 22, or the possibility of a short circuit may increase due to lithium overcharging, etc. The area of ​​the positive electrode 10 is, for example, the same as the area of ​​the positive electrode active material layer 12. The area of ​​the positive electrode 10 is, for example, the same as the area 11 of the positive electrode current collector.

[0106] 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 positive electrode 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 positive electrode 10.

[0107] The area of ​​the positive electrode 10 is smaller than the area S4 of the negative electrode current collector 21. The area 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 of ​​the negative electrode current collector 21. The area 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 of ​​the negative electrode current collector 21. The area of ​​the negative electrode current collector 21 is, for example, the same as the area of ​​the negative electrode 20. The area of ​​the negative electrode current collector 21 is, for example, the same as the area of ​​the first negative electrode active material layer 22.

[0108] In the present invention, “identical” area, length, width, thickness and / or form includes all cases having “substantially identical” area, length, width, thickness and / or form, unless the area, length, width, thickness and / or form are intentionally made to differ from one another. “Identical” area, length, width and / or thickness includes unintended differences in the area, length, width and / or thickness of the objects being compared, for example, less than 3%, less than 2%, less than 1%, less than 0.5%, or less than 0.1%.

[0109] 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.

[0110] The inert member 40 can be a gasket. By using a gasket as the inert member 40, cracks in the electrolyte layer 30 caused by the pressure difference during the pressing process can be effectively suppressed.

[0111] The inert member 40 has, for example, a single-layer structure. On the other hand, although not shown in the drawings, the inert member 40 may have a multilayer structure. In an inert member 40 having a multilayer structure, each layer may have a different composition from the others. An inert member 40 having a multilayer structure may have, for example, a two-layer, three-layer, four-layer, or five-layer structure. An inert member 40 having a multilayer structure may include, for example, one or more adhesive layers and one or more support layers. The adhesive layer effectively prevents separation between the positive electrode 10 and the electrolyte layer 30 due to volume changes of the positive electrode 10 that occur during the charging and discharging process of the all-solid-state secondary battery 10, and improves the film strength of the inert member 40 by providing bonding force between the support layer and the other layers. The support layer provides support force to the inert member 40, prevents non-uniformity of the pressure applied to the electrolyte layer 30 during the pressurizing process or charging and discharging process, and prevents deformation of the shape of the manufactured all-solid-state secondary battery 1.

[0112] The inert member 40 is, for example, a flame-retardant inert member. By providing flame retardancy, the flame-retardant inert member can prevent thermal runaway and ignition of the all-solid-state secondary battery 1. As a result, the stability of the all-solid-state secondary battery 1 is further improved. By absorbing residual moisture in the all-solid-state secondary battery 1, the flame-retardant inert member prevents deterioration of the all-solid-state secondary battery 1 and improves its lifespan characteristics.

[0113] The flame-retardant inert member includes, for example, a matrix and a filler. The matrix includes, for example, a base material and a reinforcing material. The matrix includes, for example, a fibrous base material and a fibrous reinforcing material. By including a base material in the matrix, the matrix can be elastic. Therefore, the matrix can effectively accommodate the volume change during charging and discharging of the all-solid-state secondary battery 1 and be positioned in various locations. The base material included in the matrix includes, for example, a first fibrous material. By including a first fibrous material in the base material, the volume change of the positive electrode 10 that occurs during the charging and discharging process of the all-solid-state secondary battery 1 can be effectively accommodated, and the deformation of the inert member 40 due to the volume change of the positive electrode 10 can be effectively suppressed. The first fibrous material is, for example, a material with an aspect ratio of 5 or more, 20 or more, or 50 or more. The first fibrous material is, for example, a material with an aspect ratio of 5 to 1000, 20 to 1000, or 50 to 1000. The first fibrous material is, for example, an insulating material. The first fibrous material being an insulating material effectively prevents short circuits between the positive electrode 30 and the negative electrode 20 caused by lithium dendrites and the like that generated during the charging and discharging process of the all-solid-state secondary battery 1. The first fibrous material includes, for example, one or more selected from pulp fibers, insulating polymer fibers, and ion-conducting polymer fibers. The inclusion of a reinforcing material in the matrix improves the strength of the matrix. Therefore, the matrix can prevent excessive volume changes during charging and discharging of the all-solid-state secondary battery 1 and prevent deformation of the all-solid-state secondary battery. The reinforcing material included in the matrix includes, for example, a second fibrous material. The inclusion of a second fibrous material in the reinforcing material can further uniformly increase the strength of the matrix. The second fibrous material is, for example, a material with an aspect ratio of 3 or more, 5 or more, or 10 or more. The second fibrous material is, for example, a material with an aspect ratio of 3 to 100, 5 to 100, or 10 to 100. The second fibrous material is, for example, a flame-retardant material. The second fibrous material being a flame-retardant material effectively suppresses ignition caused by thermal runaway during the charging and discharging process of the all-solid-state secondary battery 1 or by external impact. The second fibrous material is, for example, glass fiber, metal oxide fiber, or ceramic fiber.

[0114] The flame-retardant inert member contains a filler outside the matrix. The filler can be located inside the matrix, on the matrix surface, or both inside and on the surface. The filler is, for example, an inorganic material. The filler included in the flame-retardant inert member is, for example, a moisture getter. The filler prevents the degradation of the all-solid-state secondary battery 1 by removing moisture remaining inside the all-solid-state secondary battery 1 by adsorbing moisture at temperatures below 100°C. Furthermore, if the temperature of the all-solid-state secondary battery 1 rises above 150°C due to thermal runaway caused by the charging / discharging process or external shock, the filler can release the adsorbed moisture and effectively suppress ignition of the all-solid-state secondary battery 1. In other words, the filler is, for example, a flame retardant. The filler is, for example, a metal hydroxide with moisture-adsorbing properties. The metal hydroxides contained in the filler are, for example, Mg(OH)2, Fe(OH)3, Sb(OH)3, Sn(OH)4, Ti(OH)3, Zr(OH)4, Al(OH)3, or combinations thereof. The content of the filler in the flame-retardant inert member is, for example, 10-80 parts by weight, 20-80 parts by weight, 30-80 parts by weight, 40-80 parts by weight, 50-80 parts by weight, 60-80 parts by weight, or 65-80 parts by weight per 100 parts by weight of the flame-retardant inert member.

[0115] The flame-retardant inert member may further include, for example, a binder. The binder may include, for example, a curable polymer or a non-curable polymer. A curable polymer is a polymer that is cured by heat and / or pressure. A curable polymer is, for example, a solid at room temperature. The flame-retardant inert member 40 includes, for example, a heat- and pressure-curable film and / or its cured product. A heat- and pressure-curable polymer is, for example, TSA-66 from Toray Industries, Inc.

[0116] The flame-retardant inert member may further include other materials in addition to the base material, reinforcing material, filler, and binder described above. The flame-retardant inert member may further include, for example, one or more selected from paper, insulating polymer, ionic conductive polymer, insulating inorganic material, oxide-based solid electrolyte, and sulfide-based solid electrolyte. The insulating polymer may be, for example, an olefin-based polymer such as polypropylene (PP) or polyethylene (PE).

[0117] The density of the base material or reinforcing material contained 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 contained in the positive electrode active material layer 12.

[0118] The inert member 40 is a member that does not contain an electrochemically active substance, such as an electrode active material. An electrode active material is a substance that intercalates / releases lithium. The inert member 40 is a member made of a substance other than an electrode active material, which is used in the art.

[0119] [All-solid-state secondary battery] An all-solid-state secondary battery in one embodiment includes the positive electrode, the negative electrode, and an electrolyte layer disposed between the positive and negative electrodes. 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.

[0120] Referring to Figures 3 to 7, the 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.

[0121] [Positive electrode] Refer to the positive electrode mentioned above.

[0122] [Negative electrode] [Negative electrode: negative electrode active material] Referring to Figures 3 to 7, 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.

[0123] The negative electrode active material contained in the first negative electrode active layer 22 is, for example, a negative electrode material that can form an alloy or compound with lithium.

[0124] The negative electrode active material contained in the first negative electrode active material layer 22 has, for example, a particle form. The average particle size of the negative electrode active material having a particle form is, for example, 4 μm or less, 3 μm or less, 2 μm or less, 1 μm or less, 500 nm or less, 300 nm or less, or 100 nm or less. The average particle size of the negative electrode active material having a particle form is, for example, 10 nm to 4 μm, 10 nm to 3 μm, 10 nm to 2 μm, 10 nm to 1 μm, 10 nm to 500 nm, 10 nm to 300 nm, or 10 nm to 100 nm. Having an average particle size in such a range of negative electrode active material makes reversible absorption and / or desorbing of lithium during charging and discharging even easier. The average particle size of the negative electrode active material is, for example, the median diameter (D50) measured using a laser particle size analyzer.

[0125] The negative electrode active material contained in the first negative electrode active material layer 22 includes, for example, one or more selected from carbon-based negative electrode active materials and metal or semimetallic negative electrode active materials.

[0126] Carbon-based negative electrode active materials include, for example, amorphous carbon, crystalline carbon, porous carbon, or combinations thereof.

[0127] Carbon-based negative electrode active materials are particularly amorphous carbon. Amorphous carbons include, for example, carbon black (CB), acetylene black (AB), furnace black (FB), Ketjen black (KB), and graphene, but are not necessarily limited to these; any material classified as amorphous carbon in the relevant technical field can be used. Amorphous carbon is carbon that does not have crystallinity or has very low crystallinity, and is distinguished from crystalline carbon or graphite-based carbon.

[0128] The carbon-based negative electrode active material can be, for example, porous carbon. The pore volume of porous carbon is, for example, 0.1 cc / g to 10.0 cc / g, 0.5 cc / g to 5 cc / g, or 0.1 cc / g to 1 cc / g. The average pore diameter of porous carbon is, for example, 1 nm to 50 nm, 1 nm to 30 nm, or 1 nm to 10 nm. The BET specific surface area of ​​porous carbon is, for example, 100 m². 2 / g~3000m 2 It is / g.

[0129] The metallic or metalloid anode active material includes, but is not limited to, one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Any metallic or metalloid anode active material that can be used in the art to form an alloy or compound with lithium is acceptable. For example, nickel (Ni) does not form an alloy with lithium and is therefore not a metallic anode active material.

[0130] The first negative electrode active material layer 22 contains either one type of negative electrode active material or a mixture of multiple different negative electrode active materials. For example, the first negative electrode active material layer 22 contains only amorphous carbon, or one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Alternatively, the first negative electrode active material layer 22 may contain a mixture of amorphous carbon and one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). The mixing ratio of amorphous carbon and gold, etc., is by weight and is, for example, 99:1 to 1:99, 10:1 to 1:2, 5:1 to 1:1, or 4:1 to 2:1, but is not necessarily limited to these ranges and is selected according to the required characteristics of the all-solid-state secondary battery 1. Having such a composition in the negative electrode active material further improves the cycle characteristics of the all-solid-state secondary battery 1.

[0131] The negative electrode active material contained in the first negative electrode active material layer 22 includes, for example, a mixture of first particles made of amorphous carbon and second particles made of a metal or metalloid. The metal or metalloid includes, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). In other embodiments, the metalloid is a semiconductor. The content of the second particles is 1 to 99% by weight, 1 to 60% by weight, 8 to 60% by weight, 10 to 50% by weight, 15 to 40% by weight, or 20 to 30% by weight, based on the total weight of the mixture. Having the second particles in such a range of content further improves the cycle characteristics of, for example, the all-solid-state secondary battery 1.

[0132] On one hand, the first negative electrode active material layer 22 contains a composite negative electrode active material. The composite negative electrode active material may include, for example, a carbon-based support and a metal-based negative electrode active material supported on the carbon-based support. Since the composite negative electrode active material has such a structure, the uneven distribution of the metal-based negative electrode active material in the first negative electrode active material layer is prevented and a uniform distribution is 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.

[0133] 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 O y (0 < x ≤ 1, 0 < y ≤ 3), Zn x O y (0 < x ≤ 1, 0 < y ≤ 1) or may include a combination thereof. The composite of a metal and a metal oxide includes, for example, Au and Au x Oy A composite of (0 < x ≤ 2, 0 < y ≤ 3), Pt and Pt x O y A composite of (0 < x ≤ 1, 0 < y ≤ 2), Pd and Pd x O y A composite of (0 < x ≤ 1, 0 < y ≤ 1), Si and Si x O y A composite of (0 < x ≤ 1, 0 < y ≤ 2), Ag and Ag x O y A composite of (0 < x ≤ 2, 0 < y ≤ 1), Al and Al x O y A composite of (0 < x ≤ 2, 0 < y ≤ 3), Bi and Bi x O y A composite of (0 < x ≤ 2, 0 < y ≤ 3), Sn and Sn x O y A composite of (0 < x ≤ 1, 0 < y ≤ 2), Te and Te x O y (0 < x ≤ 1, 0 < y ≤ 3), Zn and Zn x O y May include a composite of (0 < x ≤ 1, 0 < y ≤ 1), or a combination thereof.

[0134] The carbon-based support is, for example, amorphous carbon. Amorphous carbon is, for example, carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), graphene, activated carbon, carbon nanofibers (CNF), carbon nanotubes (CNT), etc., but is not necessarily limited thereto, and any material classified as amorphous carbon in the relevant technical field can be used. Amorphous carbon is carbon that has no crystallinity or very low crystallinity and is distinguishable from crystalline carbon or graphite-based carbon. The carbonaceous material is, for example, a carbon-based negative electrode active material.

[0135] The composite anode active material may, for example, have a particulate form. The particle size of the composite anode active material having a particulate form may be, for example, 10 nm to 4 μm, 10 nm to 1 μm, 10 nm to 500 nm, 10 nm to 200 nm, or 10 nm to 100 nm. Having a particle size in such a range for the composite anode active material makes reversible absorption and / or desorbing of lithium during charging and discharging even easier. The metallic anode active material supported on a support may, for example, have a particulate form. The particle size of the metallic anode active material may 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, for example, have a particulate form. The particle size of the carbon-based support can be, for example, 10 nm to 2 μm, 10 nm to 1 μm, 10 nm to 500 nm, 10 nm to 200 nm, or 10 nm to 100 nm. Having a particle size range like this allows the carbon-based support to be more uniformly distributed within the first anode active material layer. The carbon-based support can be, for example, nanoparticles with a particle size of 500 nm or less. The particle size of the composite anode active material, the particle size of the metal-based anode active material, and the particle size of the carbon-based support are, for example, average particle sizes. The average particle size is, for example, the median diameter (D50) measured using a laser particle size analyzer. Alternatively, the average particle size can be automatically determined using software from electron microscope images, for example, or manually determined by hand.

[0136] [Negative electrode: Binder] The binder contained in the first negative electrode active material layer 22 is, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc., but is not necessarily limited to these, and any binder that can be used in the art can be used. The binder may consist of one or more different binders.

[0137] The inclusion of a binder in the first negative electrode active material layer 22 stabilizes the first negative electrode active material layer 22 on the negative electrode current collector 21. Furthermore, cracking of the first negative electrode active material layer 22 is suppressed despite volume changes and / or relative positional changes of the first negative electrode active material layer 22 during the charge-discharge process. For example, if the first negative electrode active material layer 22 does not contain a binder, the first negative electrode active material layer 22 can be easily separated from the negative electrode current collector 21. When the first negative electrode active material layer 22 detaches from the negative electrode current collector 21, the portion of the negative electrode current collector 21 that is exposed comes into contact with the electrolyte layer 30, increasing the likelihood of a short circuit. The first negative electrode active material layer 22 is manufactured, for example, by coating a slurry in which the materials constituting the first negative electrode active material layer 22 are dispersed onto the negative electrode current collector 21 and drying it. By incorporating a binder into the first negative electrode active material layer 22, stable dispersion of the negative electrode active material in the slurry is possible. For example, when the slurry is applied onto the negative electrode current collector 21 by screen printing, screen clogging (e.g., clogging due to aggregates of the negative electrode active material) can be suppressed.

[0138] [Negative electrode: Other additives] The first negative electrode active material layer 22 may further contain additives used in conventional all-solid-state secondary batteries 1, such as fillers, coating agents, dispersants, and ion conductivity enhancers.

[0139] [Negative electrode: solid electrolyte] The first negative electrode active material layer 22 may further contain a solid electrolyte. The solid electrolyte may be, for example, a material selected from among the solid electrolytes contained in the electrolyte layer 30. The solid electrolyte contained in the first negative electrode active material layer 22 acts as a reaction site where the formation of lithium metal is initiated within the first negative electrode active material layer 22, as a space where the formed lithium metal is stored, or as a pathway for the transfer of lithium ions. The solid electrolyte is optional.

[0140] In the first negative electrode active material layer 22, the solid electrolyte content is, for example, high in the region adjacent to the electrolyte layer 30 and low in the region adjacent to the negative electrode current collector 21. The solid electrolyte in the first negative electrode active material layer 22 may have a concentration gradient in which the concentration decreases from, for example, the region adjacent to the electrolyte layer 30 to the region adjacent to the negative electrode current collector 21.

[0141] [Negative electrode: first negative electrode active material layer] The ratio (B / A) of the initial charge capacity (B) of the first negative electrode active material layer 22 to the initial charge capacity (A) of the positive electrode active material layer is 0.005 to 0.5 or 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 (open circuit voltage) to Li / Li + The initial charge capacity of the first negative electrode active material layer 22 is determined from the second open circuit voltage (2 nd (open circuit voltage) to Li / Li + It is determined to be 0.01V.

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

[0143] If the initial charge capacity of the first negative electrode active material layer 22 is excessively small, the thickness of the first negative electrode active material layer 22 becomes very thin, so lithium dendrites formed between the first negative electrode active material layer 22 and the negative electrode current collector 21 during repeated charge-discharge processes cause the first negative electrode active material layer 22 to disintegrate, 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, the internal resistance of the 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.

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

[0145] [Negative electrode: second negative electrode active material layer] Referring to Figure 5, the all-solid-state secondary battery 1 further includes a second negative electrode active material layer 24, which is placed between, for example, the negative electrode current collector 21 and the first negative electrode active material layer 22 after charging. The second negative electrode active material layer 24 is a metallic layer containing lithium or a lithium alloy. The metallic layer contains lithium or a lithium alloy. Therefore, since the second negative electrode active material layer 24 is a metallic layer containing lithium, it acts, for example, as a lithium reservoir. Examples of lithium alloys include, but are not limited to, Li-Al alloys, Li-Sn alloys, Li-In alloys, Li-Ag alloys, Li-Au alloys, Li-Zn alloys, Li-Ge alloys, and Li-Si alloys; any alloy usable as a lithium alloy in the art can be used. The second negative electrode active material layer 24 may consist of one of these alloys or lithium, or of various types of alloys. The second negative electrode active material layer 24 is, for example, a plated layer. The second negative electrode active material layer 24 is deposited, for example, between the first negative electrode active material layer 22 and the negative electrode current collector 21 during the charging process of the all-solid-state secondary battery 1.

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

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

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

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

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

[0151] The thickness of the thin film 23 is, for example, 1 nm to 800 nm, 10 nm to 700 nm, 50 nm to 600 nm, or 100 nm to 500 nm. If the thickness of the thin film 23 is less than 1 nm, the function of the thin film 23 is difficult to achieve. If the thickness of the thin film 23 is excessively thick, the thin film 23 itself may absorb lithium, reducing the amount of lithium deposited on the negative electrode 20, which can lower the energy density of the all-solid-state battery and degrade the cycle characteristics of the all-solid-state secondary battery 1. The thin film 23 can be disposed on the negative electrode current collector 21 by, for example, vacuum deposition, sputtering, or plating, but is not limited to these methods; any method that can form the thin film 23 in the relevant art can be used.

[0152] Although not shown in the drawings, the negative electrode current collector 21 may include, for example, a base film and a metal layer disposed on one or both sides of the base film. The base film may include, for example, a polymer. The polymer may 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. By including an insulating thermoplastic polymer in the base film, the base film can soften or liquefy when a short circuit occurs, interrupting battery operation and suppressing a rapid increase in current. The metal layer may include, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or alloys thereof. The negative electrode current collector 21 may further include metal pieces and / or lead tabs. For more specific details regarding the base film, metal layer, metal chip, and lead tab of the negative electrode current collector 21, please refer to the positive electrode current collector 11 described above. Having such a structure in the negative electrode current collector 21 reduces the weight of the negative electrode 20, thereby improving the energy density of the negative electrode 20 and the lithium battery.

[0153] [Electrolyte layer] [Electrolyte layer: electrolyte] Referring to FIGS. 3 to 7, the electrolyte layer 30 includes an electrolyte disposed between the positive electrode 10 and the negative electrode 20. The electrolyte may include, for example, a solid electrolyte, a gel electrolyte, or a combination thereof.

[0154] 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.

[0155] 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 , where m, n are positive numbers, Z is one of Ge, Zn or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , where p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In, Li 7-x PS 6-x Cl x , where 0 ≦ x ≦ 2, Li 7-x PS 6-x Br x , where 0 ≦ x ≦ 2, and Li 7-x PS 6-x I xThe solid electrolyte is one or more selected from 0 ≤ x ≤ 2. Sulfide-based solid electrolytes are produced by processing starting materials such as Li2S and P2S5 by methods such as melt-quenching or mechanical milling. After such processing, heat treatment can be performed. The solid electrolyte can be amorphous, crystalline, or a mixture of both. The solid electrolyte may also contain sulfur (S), phosphorus (P), and lithium (Li) as constituent elements, for example, among the sulfide-based solid electrolyte materials mentioned above. For example, the solid electrolyte may be a material containing Li2S-P2S5. When utilizing Li2S-P2S5 as a sulfide-based solid electrolyte material to form a solid electrolyte, the molar ratio of Li2S to P2S5 is, for example, in the range of Li2S:P2S5 = 20:80~90:10, 25:75~90:10, 30:70~70:30, and 40:60~60:40.

[0156] Sulfide-based solid electrolytes may include, for example, argyrodite-type solid electrolytes represented by the following chemical formula 1: <C1> Li + 12-n-x A n+ X 2- 6-x Y - x

[0157] In the formula, A is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta, X is S, Se, or Te, Y is Cl, Br, I, F, CN, OCN, SCN, or N3, and 1 ≤ n ≤ 5 and 0 ≤ x ≤ 2. Sulfide-based solid electrolytes include, for example, 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 xThe compound may be an argyrodite-type compound containing one or more values ​​selected from 0 ≤ x ≤ 2. The sulfide-based solid electrolyte may be an argyrodite-type compound containing, for example, one or more values ​​selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0158] The density of argyrodite-type solid electrolytes can be 1.5 to 2.0 g / cc. Having a density of 1.5 g / cc or higher for argyrodite-type solid electrolytes reduces the internal resistance of all-solid-state secondary batteries, effectively suppressing penetration of the electrolyte layer by lithium.

[0159] Oxide-based solid electrolytes include, for example, Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 <x<2、0≦y<3)、BaTiO3、Pb(Zr,Ti)O3(PZT)、Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0≦x<1, 0≦y<1), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, Li3PO4, Li x Ti y (PO4)3(0 <x<2、0<y<3)、Li x Al y Ti z (PO4)3(0 <x<2、0<y<1、0<z<3)、Li 1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≦x≦1 0≦y≦1), Li x La yTiO3(0 < x < 2, 0 < y < 3), Li2O, LiOH, Li2CO3, LiAlO2, Li2O - Al2O3 - SiO2 - P2O5 - TiO2 - GeO2, Li 3+x La3M2O 12 (M = Te, Nb, or Zr, 0 ≤ x ≤ 10), or combinations thereof. The oxide-based solid electrolyte is produced, for example, by a sintering method or the like.

[0160] The oxide-based solid electrolyte is, for example, Li7La3Zr2O 12 (LLZO) and Li 3+x La3Zr 2-a M a O 12 (M doped LLZO, M = Ga, W, Nb, Ta, or Al, 0 < a < 2, 0 ≤ x ≤ 10), which is a garnet-type solid electrolyte selected therefrom.

[0161] Polymeric solid electrolytes may include, for example, a mixture of lithium salt and polymer, or a polymer having ion-conducting functional groups. Polymeric solid electrolytes may be, for example, polymeric electrolytes that are solid at 25°C and 1 atm. Polymeric solid electrolytes do not contain liquids, for example.Polymeric solid electrolytes contain polymers, such as polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), poly(styrene-β-ethylene oxide) block copolymer (PS-PEO), poly(styrene-butadiene), poly(styrene-isoprene-styrene), poly(styrene-β-divinylbenzene) block copolymer, poly(styrene-ethylene oxide-styrene) block copolymer, polystyrene sulfonate (PSS), and polyvinyl fluoride (PVF). Poly(methylmethacrylate), poly(methylmethacrylate), polyethylene glycol (PEG), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polyethylene dioxythiophene (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, SPAEKKS), sulfonated poly(aryl ether ketone) Ketone (SPAEK), poly[bis(benzimidazobenzisoquinolinones)] (SPBIBI), poly(styrene sulfonate, PSS), lithium 9,10-diphenylanthracene-2-sulfonate (DPASLi). +) or a combination thereof, but not limited to these, any lithium salt that is used in polymer electrolytes in the art is acceptable. Any lithium salt that is usable as a lithium salt in the art is acceptable. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 The polymers in the polymer solid electrolyte may be, for example, SO2 (where x and y are 1 to 20), LiCl, LiI, or mixtures thereof. The polymers contained in the polymer solid electrolyte may be compounds containing 10 or more, 20 or more, 50 or more, or 100 or more repeating units. The weight-average molecular weight of the polymers contained in the polymer solid electrolyte may be, for example, 1,000 Dalton or more, 10,000 Dalton or more, 100,000 Dalton or more, or 1,000,000 Dalton or more.

[0162] Gel electrolytes are, for example, polymer gel electrolytes. Gel electrolytes may not contain polymers and may have a gel state.

[0163] Polymer gel electrolytes may, for example, contain a liquid electrolyte and a polymer, or an organic solvent and a polymer having ionic conductive functional groups. Polymer gel electrolytes are, for example, polymer electrolytes that are in a gel state at 25°C and 1 atm. Polymer gel electrolytes may, for example, contain no liquid and be in a gel state. Liquid electrolytes used in polymer gel electrolytes may be, for example, a mixture of an ionic liquid, 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 and an ionic liquid. Polymers used in polymer gel electrolytes may be selected from polymers used in solid polymer electrolytes. Organic solvents may be selected from organic solvents used in liquid electrolytes. Lithium salts may be selected from lithium salts used in polymer solid electrolytes. Ionic liquids have a melting point below room temperature and refer to salts or molten salts that are liquid at room temperature and composed only of ions. 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 - , (C2F2SO2)2N - ,(C2F5SO2)(CF3SO2)N - , and (CF3SO2)2N -The polymer solid electrolyte may contain one or more compounds selected from among those containing one or more anions selected from the following. The polymer solid electrolyte can form a polymer gel electrolyte by, for example, impregnating a liquid electrolyte in a secondary battery. The polymer gel electrolyte may further contain inorganic particles. The polymer contained in the polymer gel electrolyte may be, for example, a compound containing 10 or more, 20 or more, 50 or more, or 100 or more repeating units. The weight-average molecular weight of the polymer contained 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.

[0164] [Electrolyte layer: Binder] The electrolyte layer 30 may, for example, contain a binder. Examples of binders included in the electrolyte layer 30 are styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but are not limited to these; any binder usable in the relevant art may be used. The binder in the electrolyte layer 30 is the same as, but may differ from, the binder in the positive electrode active material layer 12 and the negative electrode active material layer 22. The binder is optional.

[0165] The binder content of the electrolyte layer 30 is 0.1-10 wt%, 0.1-5 wt%, 0.1-3 wt%, 0.1-1 wt%, 0-0.5 wt%, or 0-0.1 wt% relative to the total weight of the electrolyte layer 30.

[0166] The present technical concept will be further explained through the following examples and comparative examples. However, these examples are for illustrative purposes only and do not limit the scope of the present technical concept.

[0167] (Manufacturing of composite cathode active materials) Example 1: Li2S-LiI-CNF, 2-stage, 10hr, 600rpm, 28G (Phase 1) Li2S and LiI were mixed in a weight ratio of 30:20. The mixture was mechanically milled using a ball mill to produce a Li2S-LiI composite. The milling conditions were 25°C and 600 rpm for 10 hours. The milling energy applied to the sample during milling was 28G.

[0168] (Phase 2) A Li2S-LiI composite and carbon nanofibers (CNF) were mixed in a weight ratio of 50:10. The mixture was mechanically milled using a ball mill to produce a Li2S-LiI-CNF composite. The milling conditions were 25°C and 600 rpm for 10 hours. The milling energy applied to the sample during milling was 28 G. The Li2S-LiI-CNF composite was used as a composite cathode active material.

[0169] The Mohs hardness of Li2S was 0.6, the Mohs hardness of LiI was 2.0, and the Mohs hardness of carbon nanofiber (CNF) was 1.5.

[0170] Example 2: Li2S-LiI-CNF, 2-stage, 8hr, 600rpm, 28G Li2S-LiI-CNF composites were manufactured using the same method as in Example 1, except that the milling time in the first and second stages was changed to 8 hours.

[0171] Example 3: Li2S-LiI-CNF, 2-stage, 6hr, 600rpm, 28G Li2S-LiI-CNF composites were manufactured using the same method as in Example 1, except that the milling time in the first and second stages was changed to 6 hours.

[0172] Example 4: Li2S-LiI-CNF, 2-stage, 4hr, 600rpm, 28G Li2S-LiI-CNF composites were manufactured using the same method as in Example 1, except that the milling time in the first and second stages was changed to 4 hours.

[0173] Comparative Example 1: Li2S-LiI-CNF, 2-stage, 1 hr, 600 rpm, 28G

[0174] Li2S-LiI-CNF composites were manufactured using the same method as in Example 1, except that the milling time in the first and second stages was changed to 1 hour.

[0175] Comparative Example 2: Li2S-LiI-CNF, 2-stage, 20hr, 600rpm, 28G Li2S-LiI-CNF composites were manufactured using the same method as in Example 1, except that the milling time in the first and second stages was changed to 20 hours.

[0176] Comparative Example 3: Li2S-LiI-CNF, 510 rpm, 10 hr, 2 stages, 20G (Phase 1) A first mixture was prepared by mixing Li2S and LiI in a weight ratio of 30:20. A Li2S-LiI composite was produced by mechanically milling the first mixture using a ball mill.

[0177] The milling conditions were 25°C and 510 rpm for 10 hours. The milling energy applied to the sample during milling was 20 G.

[0178] (Phase 2) A second mixture was prepared by mixing a Li2S-LiI composite with carbon nanofibers (CNF) in a weight ratio of 50:10. The second mixture was then mechanically milled using a ball mill to produce a Li2S-LiI-CNF composite.

[0179] The milling conditions were 25°C and 510 rpm for 10 hours. The milling energy applied to the sample during milling was 20 G. A Li2S-LiI-CNF composite was used as the composite cathode active material.

[0180] Comparative Example 4: Li2S-LiI-CNF, 300 rpm, 10 hr, 2 stages, 7G Li2S-LiI-CNF composites were manufactured in the same manner as in Example 1, except that the rotational speed was reduced in the first and second stages and the milling energy was changed to 7G.

[0181] Comparative Example 5: Li2S-LiI-CNF, 700 rpm, 10 hr, 2 stages, 38 G Li2S-LiI-CNF composites were manufactured in the same manner as in Example 1, except that the rotational speed was increased in the first and second stages and the milling energy was changed to 38G.

[0182] Comparative Example 6: Simple mixture of Li2S and CNF Li2S and carbon nanofibers (CNF) were mixed in a 30:30 weight ratio. The mixture was used as the cathode active material.

[0183] Comparative Example 7: Li2S-CNF, 600 rpm, 2 hr, 1 stage, 28 G Li2S and carbon nanofibers (CNF) were mixed in a 30:30 weight ratio. The mixture was mechanically milled using a ball mill to produce a Li2S-CNF composite. The milling conditions were 25°C and 600 rpm for 2 hours. The milling energy applied to the sample during milling was 28 G. The Li2S-CNF composite was used as a composite cathode active material.

[0184] Comparative Example 8: Li2S-CNF, 600 rpm, 10 hr, 1 stage, 28G Li2S-CNF composites were manufactured using the same method as in Comparative Example 7, except that the milling time was changed to 10 hours.

[0185] Comparative Example 9: Li2S-CNF-LiI, 600 rpm, 10 hr, 2 stages, 28G (Phase 1) Li2S and carbon nanofibers (CNF) were mixed in a weight ratio of 30:10. The mixture was mechanically milled using a ball mill to produce a Li2S-CNF composite. The milling conditions were 25°C and 600 rpm for 10 hours. The milling energy applied to the sample during milling was 28 G.

[0186] (Phase 2) A Li2S-CNF composite and LiI were mixed in a weight ratio of 40:20. The mixture was mechanically milled using a ball mill to produce a Li2S-CNF-LiI composite. The milling conditions were 25°C and 600 rpm for 10 hours. The milling energy applied to the sample during milling was 28 G. The Li2S-CNF-LiI composite was used as a composite cathode active material.

[0187] Comparative Example 10: Li2S-SE-CNF, 600 rpm, 10 hr, 2 stages, 28G (Phase 1) Li2S and Li6PS5Cl solid electrolyte (SE) were mixed in a weight ratio of 30:20. The mixture was mechanically milled using a ball mill to produce a Li2S-SE composite. The milling conditions were 25°C and 600 rpm for 10 hours. The milling energy applied to the sample during milling was 28G.

[0188] (Phase 2) Li2S-SE composite and CNF were mixed in a weight ratio of 50:10. The mixture was mechanically milled using a ball mill to produce the Li2S-SE-CNF composite. The milling conditions were 25°C and 600 rpm for 10 hours. The milling energy applied to the sample during milling was 28 G. The Li2S-SE-CNF composite was used as the composite cathode active material.

[0189] Comparative Example 11: Li2S-LiI-CNF, 600 rpm, 2 hr, 1 stage, 28G 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 produce a Li2S-LiI-CNF composite. Milling conditions were 25°C and 600 rpm for 2 hours. The milling energy applied to the sample during milling was 28G. The Li2S-LiI-CNF composite was used as a composite cathode active material.

[0190] (Manufacturing of positive electrodes and secondary batteries) Example 5 (Manufacturing of positive electrodes) A Li2S-LiI-CNF composite prepared in Example 1 was used as the positive electrode active material. Li6PS5Cl, an argyrodite-type crystalline material (D50 = 3.0 μm, crystalline), was prepared as the solid electrolyte. PTFE was prepared as the binder. These materials were mixed in a weight ratio of composite positive electrode active material:solid electrolyte:binder = 60:40:1.2 to prepare the positive electrode mixture. The positive electrode mixture was obtained by dry mixing using a ball mill.

[0191] The positive electrode was manufactured by placing the positive electrode mixture on one surface of a positive electrode current collector made of aluminum foil coated with carbon on one side, and then plate pressing it at a pressure of 200 MPa for 10 minutes. The thickness of the positive electrode was approximately 120 μm. The thickness of the positive electrode active material layer was approximately 100 μm, and the thickness of the carbon-coated aluminum foil was approximately 20 μm. The area of ​​the positive electrode active material layer and the positive electrode current collector were the same.

[0192] (Negative electrode manufacturing) A 10 μm thick stainless steel (SUS) foil was prepared as the negative electrode current collector. Carbon black (CB) with a primary particle size of approximately 30 nm and silver (Ag) particles with an average particle diameter of approximately 60 nm were prepared as the negative electrode active materials.

[0193] A mixed powder of carbon black (CB) and silver (Ag) particles in a 3:1 weight ratio was placed in a container, and 4 g of NMP solution containing 7 wt% PVDF binder (Kureha Corporation #9300) was added to prepare a mixed solution. NMP was gradually added to the prepared mixed solution while stirring to produce a slurry. The prepared slurry was applied to a SUS (stainless steel) 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 and prepare 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 area of ​​the first negative electrode active material layer and the negative electrode current collector were the same.

[0194] (Manufacturing of solid electrolyte layer) Li6PS5Cl solid electrolyte (D) is an argyrodite-type crystalline material. 50 A mixture was prepared by adding 1.5 parts by weight of an acrylic binder to 98.5 parts by weight of solid electrolyte (3.0 mm, crystalline). Octyl acetate was added to the prepared mixture while stirring to produce a slurry. The prepared slurry was applied using a bar coater onto a 15 μm thick nonwoven fabric placed on a 75 μm thick PET substrate, and dried in air at 80°C for 10 minutes to prepare a laminate. The prepared laminate was vacuum dried at 80°C for 2 hours to produce a solid electrolyte layer.

[0195] (Inert material) A slurry of cellulose fiber, glass fiber, aluminum hydroxide (Al(OH)3), an acrylic binder, and a solvent was molded into a gasket shape, and then the solvent was removed to produce a flame-retardant inert material.

[0196] 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 μm.

[0197] Before placing the manufactured flame-retardant inert material onto the solid electrolyte layer, it was subjected to vacuum heat treatment at 80°C for 5 hours to remove moisture and other contaminants from the flame-retardant inert material.

[0198] (Manufacturing of all-solid-state rechargeable batteries) Referring to Figure 3, the solid electrolyte layer was positioned on the negative electrode so that the first negative electrode active material layer was in contact with the solid electrolyte layer, and the positive electrode was positioned on the solid electrolyte layer. A gasket was placed around the positive electrode, surrounding it and in contact with the solid electrolyte layer, to prepare the laminate. The thickness of the gasket was approximately 120 μm. A flame-retardant inert material was used as the gasket. The gasket was positioned so that it was in contact with the sides of the positive electrode and the solid electrolyte layer. The positive electrode was positioned in the center of the solid electrolyte layer, with the gasket surrounding the positive electrode and extending to the end of the solid electrolyte layer. The area of ​​the positive electrode was approximately 90% of the solid electrolyte layer area, and the gasket was positioned over the remaining 10% of the solid electrolyte layer where the positive electrode was not placed.

[0199] The prepared laminate was subjected to plate press treatment at 85°C and a pressure of 500 MPa for 30 minutes. This pressurization treatment sinters the solid electrolyte layer, improving the battery characteristics. The thickness of the sintered solid electrolyte layer was approximately 45 μm. The density of the argyrodite-type crystalline Li6PS5Cl solid electrolyte contained in the sintered solid electrolyte layer was 1.6 g / cc. The area of ​​the solid electrolyte layer was the same as the area of ​​the negative electrode.

[0200] A solid-state secondary battery was manufactured by placing a pressurized laminate in a pouch and vacuum-sealing it. Parts of the positive electrode current collector and the negative electrode current collector were extended to the outside of the sealed battery and used as the positive and negative electrode terminals.

[0201] Examples 6 to 8 The positive electrode and the all-solid-state secondary battery were manufactured in the same manner as in Example 5, except that the composite positive electrode active materials manufactured in Examples 2 to 4 were used.

[0202] Comparative Examples 12 to 22 The positive electrode and the all-solid-state secondary battery were manufactured in the same manner as in Example 5, except that the composite positive electrode active materials manufactured in Comparative Examples 1 to 11 were used.

[0203] Evaluation Example 1: XRD analysis and scanning electron microscopy analysis XRD spectra were measured using CuKα radiation for the raw material (bare) Li2S used in Example 1, pulverized Li2S, the Li2S-LiI composite produced in the first step of Example 1, and the Li2S-LiI-CNF composite produced in Example 1. The measurement results are shown in Table 1 and Figure 1 below. The size and lattice constant of the Li2S crystallite were derived from the first peak for the 111 crystal plane indicated by the diffraction angle 2θ = 27° ± 2.0° in the XRD spectrum.

[0204] The pulverized 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.

[0205] The particle size of the composite (i.e., D50 particle size) and the Li2S particle size of the composite were measured for the raw material Li2S used in Example 1, the pulverized Li2S, the Li2S-LiI composite produced in the first step of Example 1, and the Li2S-LiI-CNF composite produced in Example 1 using a scanning electron microscope (SEM) and a laser particle size analyzer (PSA). The measurement results are shown in Table 1 below, Figure 2A for bare Li2S, and Figure 2B for the Li2S-LiI-CNF composite produced in Example 1.

[0206] [Table 1]

[0207] As shown in Table 1, the position of the first peak for the 111 crystal plane shown at a diffraction angle 2θ = 27° ± 2.0° of the Li2S-LiI-CNF composite of Example 1 was shifted to a lower angle compared to the position of the second peak for the 111 crystal plane shown at a diffraction angle 2θ = 27° ± 2.0° of bare Li2S. The first diffraction angle (e.g., 26.7020°) of the first peak of the Li2S-LiI-CNF composite of Example 1 was smaller than the second diffraction angle (e.g., 27.0211°) of the second peak of bare Li2S. The crystallite size (e.g., 9.86 nm, shown in FIG. 2B) of the Li2S-LiI-CNF composite of Example 1 was significantly reduced compared to the crystallite size (e.g., 64.67 nm, shown in FIG. 2A) of bare Li2S.

[0208] 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 the first-stage intermediate product of Example 1 were shifted to a lower angle compared to the position of the first peak of pulverized Li2S.

[0209] Although not shown in Table 1, the first lattice constant d1 derived from the first peak for the 111 crystal plane shown at a diffraction angle 2θ = 27° ± 2.0° of the Li2S-LiI-CNF composite of Example 1 was even larger than the second lattice constant d2 derived from the second peak for the 111 crystal plane shown at a diffraction angle 2θ = 27° ± 2.0° of bare Li2S. The first lattice constant d1 was 5.78 Å or more.

[0210] It was judged that this was because LiI was dissolved in the Li2S crystal and the lattice constant value increased. It was confirmed that the Li2S-LiI-CNF composite forms a solid solution.

[0211] Although not shown in Table 1, the first peak of the Li2S-LiI-CNF complex in Example 1 had a first half-width (FWHM1), and the second peak of bare Li2S had a second half-width (FWHM2), with the first FWHM being even larger than the second. The first FWHM1 was greater than 1°.

[0212] Although not shown in Table 1, the particle size of the composite in Example 1 was 5 μm or less.

[0213] Evaluation Example 2: XRD Analysis and Scanning Electron Microscopy Analysis

[0214] XRD spectra were measured using CuKα radiation for the composite cathode active materials (e.g., composites) produced in Examples 1 to 4 and Comparative Examples 1 to 11. The size of Li2S crystallites calculated from the first peak for the 111 crystal plane, indicated by a diffraction angle 2θ = 27° ± 2.0° in the measured XRD spectra, is shown in Table 2 below. The crystallite size was calculated using the Sherrer Equation.

[0215] The Li2S particle size of the composite cathode active materials produced in Examples 1 to 4 and Comparative Examples 1 to 11 was measured using 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 on scanning electron microscope images. The measurement results are shown in Table 2 below.

[0216] [Table 2]

[0217] In Table 2, ○ indicates the formation of a solid solution. As shown in Table 2, the Li2S-LiI-CNF composites of Examples 1 to 4 contained a Li2S-LiI solid solution, the size of the Li2S crystallites was less than 9.9 nm, and the size of the Li2S particles in the composite was 2 μm or less.

[0218] In Comparative Example 1, the Li2S-LiI-CNF composite exhibited a decrease in milling energy during manufacturing, resulting in a Li2S crystallite size more than twice that of 9.9 nm (e.g., 20.1 nm).

[0219] In Table 2, △ indicates that the solid solution was not properly formed due to the characteristics of the manufacturing conditions. For example, in Comparative Example 2, the Li2S-LiI-CNF composite underwent phase separation of LiI into a separate phase due to an increase in milling energy during manufacturing, preventing the formation of a solid solution and increasing the size of the Li2S crystallites.

[0220] In Comparative Example 4, the Li2S-LiI-CNF composite failed to form a Li2S-LiI solid solution due to an excessive decrease in milling energy during manufacturing.

[0221] In Comparative Example 5, the Li2S-LiI-CNF composite did not properly form a Li2S-LiI solid solution due to the heat generated by the increased milling energy during manufacturing.

[0222] The Li2S-LiI-CNF composite of Comparative Example 11, being manufactured in the first step, contains a Li2S-LiI solid solution, but the Li2S crystallite size increases, and the Li2S particle size of the composite exceeds 2 μm.

[0223] In Table 2, × indicates that a solid solution was not formed. For example, the simple mixture of Li2S and CNF in Comparative Example 6, the Li2S-CNF composites in Comparative Examples 5 and 6, and the Li2S-SE-LiI composite in Comparative Example 10 were unable to form a solid solution.

[0224] In Comparative Example 9, the Li2S-CNF-LiI composite was not properly formed because the Li2S-CNF composite was produced in the first step, followed by the production of the Li2S-CNF-LiI composite in the second step.

[0225] Evaluation Example 2: Charge / Discharge Test The charge-discharge characteristics of all-solid-state secondary batteries of Examples 5 to 8 and Comparative Examples 12 to 22 that employed the composite positive electrode active materials produced in Examples 1 to 4 and Comparative Examples 1 to 11 were evaluated by the following charge-discharge test.

[0226] The charge-discharge test was carried out by placing the all-solid-state secondary battery in a thermostat at 45°C.

[0227] In the first cycle, charging was performed at a constant current of .1C for 12.5 hours until the battery voltage reached 2.5V to 2.8V. Next, discharging was carried out at a constant current of 0.1C for 12.5 hours until the battery voltage reached 0.3V.

[0228] The discharge capacity of the first cycle was taken as the standard capacity. The standard capacity was shown by the specific capacity of Li2S in Table 1 below.

[0229] After the second cycle, charging and discharging were carried out under the same conditions as the first cycle up to 150 cycles. The measurement results are shown in Table 3 below. The initial efficiency is represented by the following Equation 1.

[0230] <Equation 1> Initial efficiency [%] = [Discharge capacity of the first cycle / Charge capacity of the first cycle] × 100

[0231] The number of cycles means the number of cycles required for the discharge capacity to decrease to 80% of the standard capacity after the second cycle. It was regarded that the longer the number of cycles, the better the life characteristics.

[0232]

Table 3

[0233] In Table 3, ○ indicates that a solid solution is formed. In Table 3, △ indicates that a solid solution is not properly formed due to the characteristics of the manufacturing conditions. In Table 3, × indicates that no solid solution is formed.

[0234] As shown in Table 3, the all-solid-state secondary batteries of Examples 5 to 8, which employed the composite positive electrode active materials of Examples 1 to 4, showed improved discharge capacity, initial efficiency, and life characteristics compared to the all-solid-state secondary batteries of Comparative Examples 12 to 22, which employed the composite positive electrode active materials of Comparative Examples 1 to 11.

[0235] The all-solid-state secondary battery in Comparative Example 12, which used the composite positive electrode active material of Comparative Example 1 with increased crystallite size, exhibited reduced discharge capacity and lifespan characteristics.

[0236] The all-solid-state secondary battery of Comparative Example 13, which used the composite cathode active material of Comparative Example 2, which included a separate LiI phase and had an increased crystallite size, also showed a decrease in discharge capacity and lifespan characteristics. The all-solid-state secondary batteries of Comparative Examples 14 and 15, which used the composite cathode active materials of Comparative Examples 3 and 4, which had increased crystallite size, also showed a decrease in discharge capacity and lifespan characteristics.

[0237] The all-solid-state secondary battery of Comparative Example 16, which used the composite cathode active material of Comparative Example 5, which contained a separate LiI phase and had an increased crystallite size, also showed a decrease in discharge capacity and lifespan characteristics.

[0238] In Comparative Examples 17 to 21, all-solid-state secondary batteries employing the composite positive electrode active materials of Comparative Examples 6 to 10 showed a decrease in one or more of the following characteristics: discharge capacity and lifespan.

[0239] While the all-solid-state secondary battery of Comparative Example 22, which used the composite positive electrode active material of Comparative Example 11 manufactured by performing only one-stage milling, exhibited excellent life characteristics, its discharge capacity was significantly reduced.

[0240] Although not shown in the drawings, it was confirmed that in the all-solid-state secondary batteries of Examples 5 to 8, a lithium metal layer is formed between the first negative electrode active material layer and the negative electrode current collector after initial charging. This was confirmed through cross-sectional scanning electron microscope images of the all-solid-state secondary batteries. [Industrial applicability]

[0241] In one embodiment, an all-solid-state secondary battery can be provided that has increased specific capacity and improved cycle characteristics by incorporating a composite positive electrode active material having a reduced crystallite size. [Explanation of Symbols]

[0242] 1 All-solid-state secondary battery, 10 Positive electrode, 11 Positive electrode current collector, 12 Positive electrode active material layer, 20 Negative electrode, 21 Negative electrode current collector, 22 First negative electrode active material layer, 30 Electrolyte layer, 40 Inert member

Claims

1. M ２ It contains a composite of S, alkali metal salts, and carbon-based materials. The aforementioned M is an alkali metal, and the alkali metal is Li or Na. M obtained from the XRD spectrum of the aforementioned complex ２ The size of the S crystallite is less than 9.9 nm. The composite is M ２ A composite cathode active material containing a solid solution of sulfur and an alkali metal salt.

2. The alkali metal salt is a lithium salt or a sodium salt. The alkali metal salt is a binary compound or a ternary compound. The binary compound is LiI, LiBr, LiCl, LiF, LiH, Li ２ O, Li ２ Se, Li ２ Te, Li ３ N, Li ３ P, Li ３ As, Li ３ Sb, Li ３ Al ２ , LiB ３ or includes these combinations, or NaI, NaBr, NaCl, NaF, Na ２ O, Na ２ Se, Na ３ N, Na ３ P, Na ３ As, Na ３ Sb, Na ３ Al ２ NaB ３ or a combination of these, The ternary compound is Li ３ OCl, LiPF ６ LiBF ４ LiSbF ６ LiAsF ６ LiClO ４ LiAlO ２ LiAlCl ４ LiNO ３ Li ２ CO ３ LiBH ４ Li ２ SO ４ Li ３ BO ３ Li ３ PO ４ Li ４ NCl, Li ５ NClin ２ Li ３ BN ２ Or include combinations of these, or Na ３ OCl, NaBF ４ NaPF ６ NaAsF ６ NaClO ４ NaNO ３ NaAlO ２ NaAlCl ４ NaNO ３ Na ２ CO ３ NaBH ４ Na ２ SO ４ Na ３ BO ３ Na ３ PO ４ Na ４ NCl, Na ５ NClin ２ Na ３ BN ２ A composite cathode active material according to claim 1, or comprising a combination thereof.

3. In the composite, the M ２ The composite cathode active material according to claim 1, wherein the molar ratio of S to alkali metal salt is 50:50 to 95:

5.

4. The XRD spectrum of the aforementioned complex is M ２ The first lattice constant d1 derived from the first peak, which is shown at a diffraction angle 2θ = 27° ± 2.0° corresponding to the 111 crystal plane of S, is used in the production of the composite M ２ In the XRD spectrum of S, M ２ It is even larger than the second lattice constant d2 derived from the second peak, which is shown at a diffraction angle 2θ = 27° ± 2.0° corresponding to the 111 crystal plane of S. The composite cathode active material according to claim 1, wherein the magnitude of the first lattice constant d1 is 5.78 Å or greater.

5. The first peak has a first diffraction angle, the second peak has a second diffraction angle, and the first diffraction angle is smaller than the second diffraction angle, or The first peak has a first half-width FWHM1, the second peak has a second half-width FWHM2, and the first half-width is even larger than the second half-width. The composite cathode active material according to claim 4, wherein the first half-width is 1° or more.

6. The Mohs hardness of the alkali metal salt and carbon-based material is as follows: ２ Even larger than S, The composite cathode active material according to claim 1, wherein the Mohs hardness of the alkali metal salt and the carbon-based material is 0.7 or higher.

7. The composite positive electrode active material according to claim 1, wherein the composite is in the form of particles, and the size of the composite particles is 10 μm or less.

8. The carbon-based material includes a fibrous carbon-based material, The fibrous carbon-based material comprises carbon nanostructures, and the carbon nanostructure comprises carbon nanofibers, carbon nanotubes, carbon nanobelts, carbon nanorods, or a combination thereof. The composite cathode active material according to claim 1, wherein the content of the carbon-based material is 1 to 20 wt% of the total weight of the composite.

9. M ２ The composite cathode active material according to claim 1, comprising 10 to 80 parts by weight of S, 1 to 40 parts by weight of an alkali metal salt, and 1 to 20 parts by weight of a carbon-based material.

10. The system includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, A positive electrode in which the positive electrode active material layer comprises a composite positive electrode active material and a solid electrolyte according to any one of claims 1 to 9.

11. The positive electrode active material layer comprises 100 parts by weight of the positive electrode active material layer, 40 to 90 parts by weight of the composite positive electrode active material, and 10 to 60 parts by weight of the sulfide-based solid electrolyte. The positive electrode according to claim 10, wherein the composite positive electrode active material includes a carbon-based material, and the carbon-based material is disposed only on the composite positive electrode active material in the positive electrode active material layer.

12. The invention comprises a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, as described in claim 10. An all-solid-state secondary battery in which 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.

13. The first negative electrode active material layer comprises a negative electrode active material and a binder. The all-solid-state secondary battery according to claim 12, wherein the negative electrode active material has a particle form, and the average particle size of the negative electrode active material particles is 4 μm or less.

14. The first negative electrode active material layer comprises one or more selected from carbon-based negative electrode active materials and metal or semimetallic negative electrode active materials. The carbon-based anode active material includes amorphous carbon, crystalline carbon, porous carbon, or a combination thereof. The all-solid-state secondary battery according to claim 12, wherein the metal or metalloid anode active material includes gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof.

15. The first negative electrode active material layer comprises a mixture of first particles containing amorphous carbon and second particles containing a metal or metalloid, The all-solid-state secondary battery according to claim 12, wherein the content of the second particles is 1 to 60 wt% based on the total weight of the mixture.

16. The negative electrode active material layer is further included in one or more of the following locations: between the negative electrode current collector and the first negative electrode active material layer, and between the negative electrode current collector and the electrolyte layer. The all-solid-state secondary battery according to claim 12, wherein the second negative electrode active material layer is a metal layer, and the metal layer contains lithium or a lithium alloy.

17. The electrolyte layer comprises a solid electrolyte, a gel electrolyte, or a combination thereof. The solid electrolyte includes a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof. The all-solid-state secondary battery according to claim 12, wherein the gel electrolyte includes a polymer gel electrolyte.

18. The sulfide-based solid electrolyte is Li ２ S - P ２ S ５ 、Li ２ S - P ２ S ５ - LiX, where X is a halogen element, Li ２ S - P ２ S ５ - Li ２ O, Li ２ S - P ２ S ５ - Li ２ O - LiI, Li ２ S - SiS ２ 、Li ２ S - SiS ２ - LiI, Li ２ S - SiS ２ - LiBr, Li ２ S - SiS ２ - LiCl, Li ２ S - SiS ２ - B ２ S ３ - LiI, Li ２ S - SiS ２ - P ２ S ５ - LiI, Li ２ S - B ２ S ３ 、Li ２ S - P ２ S ５ - Z ｍ S ｎ 、m, n are positive numbers, Z is one of Ge, Zn or Ga, Li ２ S - GeS ２ 、Li ２ S - SiS ２ - Li ３ PO ４ 、Li ２ S - SiS ２ - Li ｐ MO ｑ 、p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In, Li ７－ｘ PS ６－ｘ Cl ｘ 、0 ≦ x ≦ 2, Li ７－ｘ PS ６－ｘ Br ｘ 、0 ≦ x ≦ 2, and Li ７－ｘ PS ６－ｘ I ｘ , one or more selected from 0 ≤ x ≤ 2, The sulfide-based solid electrolyte comprises an argyrodite-type solid electrolyte. The argyrodite-type solid electrolyte is Li ６ PS ５ Cl, Li ６ PS ５ Br and Li ６ PS ５ Includes one or more selected from I, The all-solid-state secondary battery according to claim 17, wherein the density of the argyrodite-type solid electrolyte is 1.5 to 2.0 g / cc.

19. The positive electrode includes a positive electrode current collector, One or more of the positive electrode current collector and the negative electrode current collector include a base film and a metal layer disposed on at least one surface of the base film. The base film comprises a polymer, and the polymer comprises polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof. The all-solid-state secondary battery according to claim 13, wherein the metal layer comprises indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof.

20. The all-solid-state secondary battery according to claim 13, further comprising an inert member disposed on one side surface of the positive electrode.

Images