Positive electrode for all-solid-state battery and all-solid-state battery including the same

Abstract

A positive electrode for an all-solid-state battery in which the physical properties of the carbon-based conductive material-related components are adjusted, and an all-solid-state battery including the same are provided. The all-solid-state battery includes a positive electrode active material, a carbon-based conductive material, a binder, and an inorganic solid electrolyte, and the carbon-based conductive material is a fibrous carbon-based conductive material having a length of 1 μm to 100 μm. When the fibrous carbon-based conductive material is mixed with the positive electrode active material in an appropriate ratio, it can improve the initial discharge efficiency of the all-solid-state battery as well as the capacity retention rate during high-rate discharge of 0.5C or more.

Description

[Technical field]

[0001] The present invention relates to a positive electrode for an all-solid-state battery and an all-solid-state battery including the same. Specifically, the present invention relates to a positive electrode for an all-solid-state battery in which the physical properties of a carbon-based conductive material-related component are adjusted, and an all-solid-state battery including the same.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0185956 filed on December 27, 2022 and Korean Patent Application No. 10-2023-0095018 filed on July 21, 2023, and incorporates all contents disclosed in the documents of said Korean patent applications as part of this specification. [Background technology]

[0003] Currently, various batteries capable of overcoming the limitations of lithium secondary batteries are being researched from the viewpoints of battery capacity, safety, output, large size, ultra-small size, and the like.

[0004] Representatively, research is being continuously conducted in academia and industry on metal-air batteries, which have a much larger theoretical capacity than lithium secondary batteries, all-solid-state batteries, which are safe and have no risk of explosion, supercapacitors in terms of output, NAS batteries or RFBs (redox flow batteries) in terms of large size, and thin film batteries in terms of ultra-miniaturization.

[0005] Of these, all-solid-state batteries refer to batteries in which the liquid electrolyte used in conventional lithium secondary batteries is replaced with a solid, and since no flammable solvent is used in the battery, there is absolutely no risk of fire or explosion due to the decomposition reaction of conventional electrolytes, which greatly improves safety. In addition, because Li metal or Li alloy can be used as the anode material, there is an advantage in that the energy density relative to the mass and volume of the battery is dramatically improved.

[0006] In particular, inorganic solid electrolytes among the types of solid electrolytes in all-solid-state batteries can be divided into sulfide-based and oxide-based. The solid electrolyte that has been most developed at present is the sulfide-based solid electrolyte, which has the advantages of higher ionic conductivity and a wider operating temperature range than other solid electrolytes. Unlike conventional lithium secondary batteries, all-solid-state batteries containing sulfide-based solid electrolytes do not conduct Li ions through liquid electrolytes, so when manufacturing the positive electrode, it is necessary to increase the contact interface between the positive electrode active material and the electrolyte by adding small particle size sulfide-based solid electrolyte to the inside of the positive electrode to increase the conductivity of Li ions. In addition, it is necessary to add a conductive material for electron conduction between the active material and the electrolyte and other battery elements in the positive electrode, but decomposition of the sulfide-based solid electrolyte due to excessive electron transfer during charging and discharging may occur.

[0007] Therefore, the present inventors have grasped the physical property factors of carbon-based conductive materials that can be used for the positive electrodes of all-solid-state batteries, particularly inorganic all-solid-state batteries, and have studied methods for improving the performance of all-solid-state batteries mainly using carbon-based conductive materials, and have completed the present invention. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Korean Patent Publication No. 10-2022-0028933 Summary of the Invention [Problem to be solved by the invention]

[0009] The object of the present invention is to provide a positive electrode for an all-solid-state battery in which the physical properties of a carbon-based conductive material-related component are adjusted in order to improve the performance of the positive electrode for the all-solid-state battery, and an all-solid-state battery including the same. [Means for solving the problem]

[0010] According to a first aspect of the present invention, The present invention provides a positive electrode for an all-solid-state battery, comprising a positive electrode active material, a carbon-based conductive material, and an inorganic solid electrolyte.

[0011] In one embodiment of the present invention, the carbon-based conductive material is a fibrous carbon-based conductive material having a length of 1 μm to 100 μm.

[0012] In one embodiment of the present invention, the carbon-based conductive material is a fibrous carbon-based conductive material having a diameter of 50 nm to 500 nm.

[0013] In one embodiment of the present invention, the BET specific surface area of ​​the carbon-based conductive material is 2 / g~20m 2 / g.

[0014] In one embodiment of the present invention, the powder resistivity of the carbon-based conductive material is 0.025 Ω·cm or less under a pressure of 196 MPa.

[0015] In one embodiment of the present invention, the density of the carbon-based conductive material is 1 g / cm 3 ~5g / cm 3 It is.

[0016] In one embodiment of the present invention, the carbon-based conductive material has an A value of 100-500.

[0017] In one embodiment of the present invention, the carbon-based conductive material is characterized by the fact that, in Raman spectroscopy, I D / I G The difference in values ​​is between 0.3 and 0.7.

[0018] In one embodiment of the present invention, the carbon-based conductive material has a difference in degree of graphitization (DoG) value between before and after graphitization of 10 to 50 in XRD analysis.

[0019] In one embodiment of the invention, the positive electrode has a B value of 5-50.

[0020] In one embodiment of the present invention, the positive electrode active material is LiCoO2, LiNiO2, LiMnO2, Li2MnO3, LiMn2O4, Li(Ni a Co b Mn c)O2(0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), LiNi 1-y Co y O2(0 < y < 1), LiCo 1-y Mn y O2(0 < y < 1), LiNi 1- yMnyO2(0 < y < 1), Li(Ni a Co b Mn c )O4(0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2), LiMn 2-z Ni z O4(0 < z < 2), LiMn 2-z Co z O4(0 < z < 2) and is selected from the group consisting of these combinations.

Advantages of the Invention

[0021] In manufacturing the positive electrode for an all - solid - state battery, by adjusting the physical properties of the carbon - based conductive material - related components within a specific range, the performance of the positive electrode for an all - solid - state battery can be improved. Specifically, a fibrous carbon - based conductive material with specific physical properties, when mixed with the positive electrode active material in an appropriate ratio and used, can not only improve the initial discharge efficiency of the all - solid - state battery as much as possible, but also improve the capacity retention rate during high - rate discharge at 0.5C or more.

Brief Description of the Drawings

[0022] [Figure 1] It is a graph showing the results of the capacity retention rate in the 1st to 3rd charge - discharge tests according to the experimental examples.

Modes for Carrying Out the Invention

[0023] The specific examples provided by the present invention can all be achieved by the following description. The following description should be understood as describing the preferred specific examples of the present invention, and it should be understood that the present invention is not necessarily limited thereto.

[0024] Unless the measurement conditions and methods are specifically described for the physical properties described in this specification, the physical properties are measured according to the measurement conditions and methods commonly used by those of ordinary skill in the art.

[0025] One aspect of the present invention provides a positive electrode for an all-solid-state battery, the positive electrode comprising a positive electrode active material, a conductive material, and an inorganic solid electrolyte. According to one embodiment of the present invention, the positive electrode for an all-solid-state battery further comprises a binder. The conductive material is a carbon-based conductive material mainly composed of carbon, which is commonly used as a component of conductive materials in the art. Even if there is no special reference to the material of the conductive material in this specification, it is interpreted as a carbon-based conductive material. The positive electrode uses a fibrous conductive material having specific physical properties mixed with the positive electrode active material in an appropriate ratio, thereby improving the performance of the all-solid-state battery, specifically, the initial discharge efficiency and the capacity retention rate during high-rate discharge.

[0026] In one embodiment of the positive electrode of the present invention, the conductive material includes a fibrous conductive material. As used herein, a fibrous conductive material refers to a conductive material having a cylindrical shape with an aspect ratio, calculated by dividing the length of the cylinder by the diameter of the circle, of 5 or more.

[0027] According to one embodiment of the present invention, the fibrous conductive material has a length of 1 μm to 100 μm. Specifically, the length of the fibrous conductive material is 1 μm or more, 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, and 100 μm or less, 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, and may be 1 μm to 100 μm, 3 μm to 60 μm, or 5 μm to 20 μm. When the length of the fibrous conductive material is adjusted within the above range, it may bring about an effect of forming an appropriate conductive network between active materials, which may be advantageous for improving the performance of an all-solid-state battery.

[0028] According to one embodiment of the present invention, the fibrous conductive material has a diameter of 50 nm to 500 nm. The diameter is a value measured with respect to a circular cross section of the fibrous conductive material. Specifically, the diameter of the fibrous conductive material is 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm or more, and 500 nm or less, 470 nm or less, 440 nm or less, 410 nm or less, 380 nm or less, 350 nm or less, and may be 50 nm to 500 nm, 70 nm to 410 nm, or 100 nm to 350 nm. When the diameter of the fibrous conductive material is adjusted within the above range, it may bring about an effect such as ensuring a sufficient amount of active material while appropriately disposing the conductive material therebetween, which may be advantageous for improving the performance of an all-solid-state battery.

[0029] According to one embodiment of the present invention, the fibrous conductive material has an aspect ratio of 20 or more. The aspect ratio means a value obtained by dividing the length of a cylinder by the diameter of a circle in a cylindrical fibrous conductive material. Specifically, the aspect ratio of the fibrous conductive material may be 20 or more, 22 or more, 24 or more, 26 or more, 28 or more, 30 or more, 32 or more, 34 or more, 36 or more, 38 or more, or 40 or more. As long as the fibrous conductive material is effectively disposed between the active materials, the upper limit of the aspect ratio of the fibrous conductive material is not particularly limited, but for example, the aspect ratio of the fibrous conductive material may be 100 or less. When the aspect ratio of the fibrous conductive material is adjusted within the above range, it may bring about an effect such as the conductive material being effectively disposed between the active materials, which may be advantageous for improving the performance of the all-solid-state battery.

[0030] According to one embodiment of the present invention, the conductive material is 1 m 2 / g~20m 2 The BET specific surface area is a specific surface area measured based on the BET method, and can be calculated from the mass gas adsorption amount at liquid nitrogen temperature (77K) using, for example, BELSORP-mini II manufactured by BEL Japan. Specifically, the BET specific surface area of ​​the conductive material is 2 / g or more, 2m 2 / g or more, 3m 2 / g or more, 4m 2 / g or more, 5m2 / g or more, and 2 / g or less, 19m 2 / g or less, 18m 2 / g or less, 17m 2 / g or less, 16m 2 / g or less, 15m 2 / g or less, and 1m 2 / g~20m 2 / g, 3m 2 / g~17m 2 / g, 5m 2 / g~15m 2 When the BET specific surface area of ​​the conductive material is adjusted within the above range, it may be advantageous for improving the performance of the all-solid-state battery by providing an effect such as efficient contact of the conductive material with the active material in relation to the input amount.

[0031] According to an embodiment of the present invention, the conductive material has a powder resistivity of 0.025 Ω·cm or less under a pressure of 196 MPa. The conductivity of the conductive material can be measured as the powder resistivity of the conductive material powder, and the powder resistivity can be measured by adjusting the pressure applied to the powder using a powder resistivity meter equipped with a 4-pin probe. For example, the powder resistivity can be measured by putting a certain amount of conductive material into a powder resistivity meter, continuously applying a force, and measuring the density measured when the particles are pressed, thereby measuring the rolled density, and the powder resistivity at this time is measured using the 4-pin probe. The conductive material according to an embodiment of the present invention may have a reduced powder resistivity as the rolled density increases, which means that the conductivity of the conductive material particles themselves improves as the degree of compression increases. Specifically, the powder resistivity of the conductive material may be 0.025 Ω·cm or less, 0.024 Ω·cm or less, 0.023 Ω·cm or less, 0.022 Ω·cm or less, 0.021 Ω·cm or less, or 0.02 Ω·cm or less under a pressure of 196 MPa. The conductive material according to the present invention has low powder resistivity and excellent conductivity.

[0032] According to one embodiment of the present invention, the conductive material has a density of 1 g / cm 3 ~5g / cm 3The density means the true density of the conductive material, and can be measured according to a conventional measuring method in the art. For example, the density can be measured using an AccuPycII-1340 device manufactured by Micromeritics. Specifically, the density of the conductive material is 1 g / cm 3 More than 1.5g / cm 3 More than 2g / cm 3 More than 5g / cm 3 Below 4.5g / cm 3 Below, 4g / cm 3 Below 3.5g / cm 3 Below 3g / cm 3 2.5g / cm3 or less, 1g / cm 3 ~5g / cm 3 , 1.5g / cm 3 Up to 4g / cm 3 , 2g / cm 3 ~2.5g / cm 3 When the density of the conductive material is adjusted within the above range, it may bring about effects such as improved functionality of the conductive material, which may be advantageous for improving the performance of the all-solid-state battery.

[0033] The positive electrode for the all-solid-state battery can be advantageously adjusted to improve the performance of the all-solid-state battery by confirming the relationship of various physical properties with the conductive material. In this regard, in one embodiment of the present invention, a new parameter A is defined in relation to the physical properties of the conductive material. The value of A is determined by the following Equation 1.

[0034] A = specific surface area x length x density [Formula 1]

[0035] Here, the specific surface area is the BET specific surface area (m 2 / g), length is the length of the conductive material (μm), and density is the density of the conductive material (g / cm 3). The length means the length of the conductive material, but in the case of a spherical conductive material such as a particulate conductive material, it may mean the diameter of the sphere. The specific surface area, length and density, which are factors that determine the value of A, are numerical values ​​in the above units, and therefore the unit of the value of A is not particularly converted. According to one embodiment of the present invention, the conductive material has a value of A of 100 to 500. Specifically, the value of A of the conductive material is 100 or more, 110 or more, 120 or more, 130 or more, 140 or more, or 150 or more, and is 500 or less, 470 or less, 440 or less, 410 or less, 380 or less, or 350 or less, and may be 100 to 500, 130 to 410, or 150 to 350. The value of A of the conductive material may be one criterion for whether the conductive material can exhibit functionality in the positive electrode of an all-solid-state battery. In the case of a linear conductive material such as the well-known carbon nanofiber, the conductive material existing in a long fiber form faces the active material and electrolyte particles in the fiber direction, while in the case of a dot-like conductive material such as carbon black, each particle faces the active material and electrolyte. In this case, the value of A is a variable that represents the shape of the conductive material, and means a shape including a hollow structure on the surface of the conductive material. According to the above formula 1, when the conductive material used is linear, the value of A increases as the length on the fiber increases and the density increases. The longer the length of each fiber, the smaller the contact between the conductive material fibers or particles and the less likely they are to aggregate, thereby increasing the dispersibility of the conductive material in the positive electrode. When the value of A of the conductive material is adjusted within the above range, the conductive material can exhibit sufficient functionality in the positive electrode, which may be advantageous for improving the performance of the all-solid-state battery.

[0036] According to one embodiment of the present invention, the carbon-based conductive material is characterized by the I D / I G The difference between the values ​​is 0.3 to 0.7. D / I G The value can be measured according to a method commonly used in the art, specifically, according to the method described in the Examples below. D / I G The difference in values ​​is the I D / I GThe value is expressed by subtracting the lower value from the higher value. Specifically, the I D / I G The difference in value may be 0.3 or more, 0.35 or more, 0.4 or more, 0.45 or more, 0.7 or less, 0.65 or less, 0.6 or less, 0.55 or less, 0.5 or less, and may be 0.3 to 0.7, 0.35 to 0.65, or 0.4 to 0.6. The carbon-based conductive material has a certain level of change in crystallinity due to graphitization, and the conductive material before graphitization is easily harmonized with the positive electrode active material and the electrolyte.

[0037] According to an embodiment of the present invention, the carbon-based conductive material has a difference in degree of graphitization (DoG) value between before and after graphitization in XRD analysis of 10 to 50. The graphitization method and the method of measuring the degree of graphitization (DoG) value may be performed according to a method commonly used in the art, specifically, according to the method described in the following examples. The degree of graphitization (DoG) is an index for determining which material the crystal plane of a sample is closer to, between the crystal plane spacing of ideal graphite (3.354 Å) and the crystal plane spacing of coal (3.440 Å). In the case of amorphous carbon having a spacing wider than the crystal plane spacing of coal, the degree of graphitization (DoG) value appears as a negative number, and the closer to 100, the more completely aligned the graphite is. The difference in the degree of graphitization (DoG) value is represented by subtracting the lower value from the higher value of the degree of graphitization (DoG) values ​​before and after graphitization. Specifically, the difference in degree of graphitization (DoG) value before and after graphitization of the carbon-based conductive material is 10 or more, 15 or more, 20 or more, or 25 or more, and may be 50 or less, 45 or less, 40 or less, 35 or less, or 30 or less, or may be 10 to 50, 15 to 45, or 20 to 40. The carbon-based conductive material has a certain level of crystallinity change due to graphitization, so that the conductive material before graphitization is easily harmonized with the positive electrode active material and the electrolyte.

[0038] The positive electrode active material can be used without limitation as long as it can be used as a positive electrode active material for a lithium secondary battery. For example, the positive electrode active material may be a lithium transition metal oxide containing one or more transition metals. In one specific example of the present invention, the positive electrode active material is LiCoO2, LiNiO2, LiMnO2, Li2MnO3, LiMn2O4, Li(Ni a Co b Mn c )O2(0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), LiNi 1-y Co y O2(0 < y < 1), LiCo 1-y Mn y O2(0 < y < 1), LiNi 1-y Mn y O2(0 < y < 1), Li(Ni a Co b Mn c )O4(0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2), LiMn 2-z Ni z O4(0 < z < 2), LiMn 2-z Co z O4(0 < z < 2) and is selected from the group consisting of combinations thereof.

[0039] The binder binds the electrode components such as the positive electrode active material and the conductive material, thereby supporting the electrode to have a stable internal structure. The solid electrolyte mainly used in one embodiment of the present invention is a sulfide-based solid electrolyte, which has a moisture-sensitive property such as generating H2S gas when in contact with moisture, and therefore it is preferable to remove moisture as much as possible during the manufacture of the electrode. According to one embodiment of the present invention, the binder is an organic binder. The organic binder refers to a binder that dissolves or disperses in an organic solvent, particularly N-methylpyrrolidone (NMP), and is distinguished from an aqueous binder that uses water as a solvent or dispersion medium. Specifically, the organic binder may be selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyimide, polyamide-imide, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butylene rubber, and fluororubber, but is not limited thereto.

[0040] When a dry method is used to bind electrode components such as a positive electrode active material and a conductive material with a binder, a fiberized binder may be used. The fiberized binder is fibrous and connects components in the electrode over a wide range within the electrode structure, so that the basic structure of the electrode can be maintained with only the positive electrode active material, the conductive material, and the binder. The fiberized binder is not particularly limited as long as it is commonly used in the technical field, and for example, the fiberized binder may be polytetrafluoroethylene (PTFE). The fiberized binder may be used in combination with the organic binder.

[0041] In the all-solid-state battery, the solid electrolyte is not particularly limited as long as it is a solid electrolyte generally used in the technical field. According to one embodiment of the present invention, in the all-solid-state battery, the solid electrolyte includes an inorganic solid electrolyte, and the inorganic solid electrolyte is a sulfide-based solid electrolyte, a halide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof.

[0042] The sulfide-based solid electrolyte is an electrolyte component containing sulfur atoms, and is not limited to a specific component, and may include one or more of a crystalline solid electrolyte, a non-crystalline solid electrolyte (a glassy solid electrolyte), and a glass ceramic solid electrolyte. Specific examples of the sulfide-based solid electrolyte include an LPS-type sulfide containing sulfur and phosphorus (e.g., Li6PS5Cl), Li 4-x Ge 1-x P x S4 (x is 0.1 to 2, specifically, x is 3 / 4, 2 / 3), Li 10±1 MP2X 12 (M=Ge, Si, Sn, Al, X=S, Se), Li 3.833 Sn 0.833 As 0.166 S4, Li4SnS4, Li 3.25 Ge 0.25 P 0.75 S4, Li2S-P2S5, B2S3-Li2S, xLi2S-(100-x)P2S5 (x is 70 to 80), Li2S-LiI-P2S5, Li2S-LiI-L i2O-P2S5, Li2S-LiBr-P2S5, Li2S-LiC1-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S -P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-A12S3, Li2S-GeS2, Li2S-GeS2-ZnS, Li2S-SiS2-Li3N, Li2S-SiS2-LiI, Li2S-B2S3-LiI, and the like, but are not necessarily limited to these.

[0043] The halide-based solid electrolyte is Li3YC16 and Li3YB r6It may include at least one of the above, but is not necessarily limited to this.

[0044] The oxide-based solid electrolyte is, for example, Li 3x La 2 / 3-x LLT series with perovskite structure such as TiO3, Li 14 LISICON, Li such as Zn(GeO4)4 1.3 Al 0.3 Ti 1.7 LATP system such as (PO4)3, (Li 1+x Ge 2-X Al x The catalyst may be selected appropriately from LAGP-based catalysts such as (PO4)3) and phosphate-based catalysts such as LiPON, and is not necessarily limited to these.

[0045] The positive electrode active material, conductive material, binder, and inorganic solid electrolyte constituting the positive electrode for the all-solid-state battery may be introduced into the positive electrode in various ways and forms. The positive electrode active material, conductive material, binder, and inorganic solid electrolyte may be mixed at once to manufacture the positive electrode, or the positive electrode active material, conductive material, and binder may be used to form a structure of the all-solid-state battery in advance, and then the inorganic solid electrolyte may be injected and fixed.

[0046] The positive electrode active material, the conductive material, and the binder may be granulated to form a structure of an all-solid-state battery. The granules may be prepared by a method commonly used in the art, and are not particularly limited. For example, the granules may be prepared by preparing a slurry and then spray drying the slurry. The active material, which is a powdered fine particle, is added together with the binder and the conductive material to grow the size of the granules to a specific level. According to one embodiment of the present invention, the granules are spherical particles including the positive electrode active material, the binder, and the solid electrolyte. The term "spherical" does not mean a perfect sphere in the strict sense, but is generally used as a comprehensive concept including round particles.

[0047] According to one embodiment of the present invention, the granules are spherical particles having a diameter of 30 μm to 150 μm. Here, the spherical particles do not mean perfectly spherical particles, so the diameter means the largest value among the distances from any one fulcrum on the particle surface to another fulcrum on the surface. Specifically, the diameter of the granules is 30 μm or more, 35 μm or more, 40 μm or more, 45 μm or more, 50 μm or more, 150 μm or less, 145 μm or less, 140 μm or less, 135 μm or less, 130 μm or less, 125 μm or less, 120 μm or less, and may be 30 μm to 150 μm, 40 μm to 135 μm, 50 μm to 120 μm. When the size of the granules is adjusted within the above range, an appropriate level of voids capable of accommodating a solid electrolyte can be secured when an active material layer is formed.

[0048] The positive electrode active material, conductive material, and binder are introduced into the positive electrode by adjusting the mixing ratio to a level where the functionality of the conductive material and the binder is sufficiently adjusted while containing as much positive electrode active material as possible to ensure the capacity of the electrode. According to one embodiment of the present invention, the positive electrode contains 83 to 99.8 parts by weight of the positive electrode active material, 0.1 to 10 parts by weight of the binder, and 0.01 to 10 parts by weight of the conductive material, based on 100 parts by weight of the total weight of the positive electrode active material, the binder, and the conductive material. Specifically, the content of the positive electrode active material is 83 parts by weight or more, 84 parts by weight or more, 85 parts by weight or more, 86 parts by weight or more, 87 parts by weight or more, 88 parts by weight or more, 89 parts by weight or more, 90 parts by weight or more, and 99.9 parts by weight or less, 99.8 parts by weight or less, 99.7 parts by weight or less, 99.6 parts by weight or less, 99.5 parts by weight or less, 99.4 parts by weight or less, 99.3 parts by weight or less, based on 100 parts by weight of the total weight of the positive electrode active material, the binder, and the conductive material. The content of the binder is 0.1 parts by weight or more, 0.2 parts by weight or more, 0.3 parts by weight or more, 0.4 parts by weight or more, 0.5 parts by weight or more, and 10 parts by weight or less, 9.5 parts by weight or less, 9 parts by weight or less, 8.5 parts by weight or less, 8 parts by weight or less, 7.5 parts by weight or less, based on 100 parts by weight of the total weight of the positive electrode active material, the binder, and the conductive material. The content of the conductive material is 0.01 parts by weight or more, 0.05 parts by weight or more, 0.1 parts by weight or more, 0.2 parts by weight or more, 0.3 parts by weight or more, 0.4 parts by weight or more, 0.5 parts by weight or more, and 10 parts by weight or less, 9.5 parts by weight or less, 9 parts by weight or less, 8.5 parts by weight or less, 8 parts by weight or less, 8 parts by weight or less, 7.5 parts by weight or less, based on 100 parts by weight of the total weight of the positive electrode active material, binder, and conductive material. When the contents of the positive electrode active material, binder, and conductive material are adjusted within the above ranges, it may be advantageous to improve the performance of the battery.

[0049] The performance of the all-solid-state battery positive electrode can be improved by adjusting the physical properties of the conductive material in consideration of the ratio of the conductive material to the positive electrode active material. In this regard, in one embodiment of the present invention, a new parameter B is defined in relation to the conductive material and the positive electrode active material. The value of B is determined by the following Equation 2.

[0050] B=R×A [Formula 2]

[0051] Here, R is a value obtained by dividing the weight of the conductive material by the weight of the positive electrode active material based on the positive electrode, and A is a value calculated by the above-mentioned Equation 1. The value of R is a value obtained by dividing the same unit weight of the conductive material and the positive electrode active material, so there is no unit, and the value of A is also a numerical value without converting the unit as described above. Therefore, the value of B also has no particular unit. According to one embodiment of the present invention, the conductive material has a value of B of 5 to 50. Specifically, the value of B of the conductive material is 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, or 10 or more, and is 50 or less, 46 or less, 42 or less, 38 or less, 34 or less, or 30 or less, and may be 5 to 50, 8 to 38, or 10 to 30. The value of B of the conductive material contributes to improving the performance of the all-solid-state battery by providing a standard that can appropriately impart conductivity to the positive electrode active material that plays an important role in the performance such as the capacity of the all-solid-state battery. When the value of B of the conductive material is adjusted within the above range, the conductive material may exhibit sufficient functionality in the positive electrode, which may be advantageous for improving the performance of the all-solid-state battery.

[0052] The positive electrode active material, conductive material, binder, and inorganic solid electrolyte may be laminated on a current collector to form a sheet-shaped positive electrode active material layer. When the positive electrode active material layer is formed on the current collector, the positive electrode includes the current collector and the positive electrode active material layer. The current collector contacts the positive electrode active material layer over a larger area, thereby effectively transferring electrons to the positive electrode active material layer. The current collector is electrically conductive, such as a metal plate, and an electrode known in the art may be appropriately used depending on the polarity of the battery.

[0053] One aspect of the present invention provides an all-solid-state battery including the above-described positive electrode for an all-solid-state battery. In constructing the all-solid-state battery, in addition to the solid electrolyte contained in the positive electrode, another solid electrolyte layer may be introduced between the positive electrode and the negative electrode, and such a solid electrolyte layer can play a role parallel to that of a separator in a general lithium secondary battery. The above-described battery may sometimes use a liquid electrolyte together to be utilized as a semi-solid battery, and in such a case, another polymer separator may be further required.

[0054] The polymer separator is interposed between the negative electrode and the positive electrode, and serves to electrically insulate the negative electrode and the positive electrode while allowing lithium ions to pass through. Any polymer separator membrane that can be used in the normal all-solid-state battery field can be used, and there is no particular limitation.

[0055] The negative electrode corresponding to the positive electrode contains a negative electrode active material. Any material that can be used as a negative electrode active material for a lithium ion secondary battery can be used as the negative electrode active material. For example, the negative electrode active material is carbon such as non-graphitizable carbon and graphite-based carbon; Li x Fe2O3 (0 ≦ x ≦ 1), Li x WOx2 (0 ≦ x ≦ 1), Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) and other metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; titanium oxides; lithium titanium oxides, etc. One or more selected from the above can be used.

[0056] The negative electrode may be manufactured in the form of an anodeless battery in which no lithium is present initially. In the anodeless battery, the negative electrode active material such as lithium metal or lithium alloy, which can be a lithium supply source, is not present in the negative electrode when the battery is first assembled, but lithium may be precipitated in the negative electrode upon charging, and then charging and discharging may be performed. Therefore, in the anodeless battery, the negative electrode active material may be located outside the negative electrode, and the initial negative electrode active material layer may not contain lithium, but may use a carbon-based material in which lithium ions can move inside.

[0057] The negative electrode may include a conductive material and a binder depending on the type of negative electrode active material, and the conductive material and binder used in the negative electrode may be any material that can be used as a conductive material and a binder in a negative electrode of a lithium secondary battery in the art. Specifically, the conductive material and binder may be selected from the range of the conductive material and binder used in the positive electrode.

[0058] Among the configurations of the all-solid-state battery, configurations that are not specifically disclosed in this specification follow methods commonly used in the technical field.

[0059] One aspect of the present invention provides a battery module including the all-solid-state battery as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source.

[0060] Specific examples of the device include, but are not limited to, power tools that are powered by an electric motor; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc.; electric two-wheeled vehicles, including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and power storage systems.

[0061] In the following, preferred examples are shown to aid in understanding the present invention. However, the following examples are provided to facilitate understanding of the present invention, and the present invention is not limited thereto.

[0062] Example (composite positive electrode for all-solid-state battery) Example 1 LiNi as active material 0.8 Co 0.1 Mn O.1 Powder was prepared by mixing O2 (NCM 811), a sulfide-based all-solid electrolyte (LPSC1) as an electrolyte, and an example conductive material 1, a fibrous carbon-based conductive material, in a weight ratio of 60:35:5. 1.2 g of the positive electrode active material and 0.7 g of the sulfide-based all-solid electrolyte were measured in powder form and mixed for 15 minutes using an agate mortar in a dry room environment. Then, 0.1 g of example conductive material 1 was measured and added to the mixture, and mixed for an additional 15 minutes to prepare a composite positive electrode in the form of a mixed powder.

[0063] Example 2 A composite positive electrode was produced in the same manner as in Example 1, except that an example conductive material 2, which was a fibrous carbon-based conductive material, was used as the conductive material.

[0064] Example 3 A composite positive electrode was produced in the same manner as in Example 1, except that an example conductive material 3, which was a fibrous carbon-based conductive material, was used as the conductive material.

[0065] Comparative Example 1 A composite positive electrode was produced in the same manner as in Example 1, except that comparative conductive material 1, which was a particulate carbon-based conductive material, was used as the conductive material.

[0066] Comparative Example 2 A composite positive electrode was produced in the same manner as in Example 1, except that comparative conductive material 2, which was a particulate carbon-based conductive material, was used as the conductive material.

[0067] Comparative Example 3 A composite positive electrode was produced in the same manner as in Example 1, except that comparative conductive material 3, which was a particulate carbon-based conductive material, was used as the conductive material.

[0068] The example conductive materials and comparative conductive materials have the physical properties shown in Table 1 below.

[0069] [Table 1]

[0070] *BET specific surface area (m 2 / g): Measured using a BET specific surface area measuring device (manufacturer: Nippon Bell, product: BEL_SORP_MAX) by degassing at 200°C for 8 hours and then performing N2 adsorption / desorption at 77K.

[0071] *Diameter (μm): After manufacturing the fibrous conductive material and particulate conductive material, they are dispersed in an organic solvent, and optical images are taken and statistically measured using a particle image analyzer (manufacturer: Shimadzu, product: iSpect DIA-10). The diameter of the conductive material is the average value after measuring the diameters of more than 100 conductive fibers / particles within the image.

[0072] *Length (μm): After manufacturing the fibrous conductive material, it is dispersed in an organic solvent, and optical images are taken and statistically measured using a particle image analyzer. The length of the conductive material is the average value after measuring the diameters of more than 100 conductive fibers / particles within the image.

[0073] *Density (g / cm 3 ): The density of carbon-based conductive materials is measured using a pycnometer (manufacturer: Micromeritics, product: AccuPycII-1340) that can measure the density of solid samples. A conductive material measurement sample with a known weight is placed in the sample chamber of the pycnometer, helium or nitrogen gas is injected, and the volume occupied by the sample is calculated to measure the density.

[0074] *Powder resistance (Ω·cm): Measure the powder resistance of a solid conductive material sample using a powder resistance meter (manufacturer: Hantech, product: HPRM-FA2). After attaching a lower punch to the body of the powder resistor mold, measure the conductive material measurement sample (whose weight is known), attach an upper punch, and place it inside the powder resistance meter. Then, operate the device to apply pressure from 0 to 2000kgf in 400kgf increments, and observe the final resistance at 2000kgf (196MPa).

[0075] The experimental conductive materials and comparative conductive materials were analyzed by Raman spectrum and XRD (X-ray diffraction) before and after graphitization, and the results are shown in Table 2 below.

[0076] [Table 2]

[0077] *Graphitization: A retort box containing 10g of carbon-based conductive material to be graphitized was placed inside the heating chamber of a carbon fiber graphitization furnace (operating temperature: 2200~2800℃), and the temperature was raised while injecting argon or nitrogen gas under vacuum conditions, heating up to a maximum of 2800℃, and then cooled for 18 hours or more to obtain graphitized carbon-based conductive material. When the temperature was raised, the heating rate was gradually reduced for each temperature range to prevent overheating or thermal runaway.

[0078] *I D / I G Using a Raman spectrometer (manufacturer: Jasco, product: NRS-2000B), Raman spectra were obtained for the surface of the sample using a 532 nm laser, and the average spectrum for 50 points was analyzed and measured. D / I G The value of 1560 to 1580 cm was obtained by Raman spectroscopy. -1 The intensity value of the peak in the absorption region of G ) to 1320 to 1350 cm-1 The intensity value of the peak in the absorption region of D ) is the ratio of

[0079] *△I D / I G :I after graphitization D / I G -I before graphitization D / I G *Crystal plane d(002): The conductive material sample to be measured was attached to an XRD analyzer (manufacturer: Bruker, product: D8 Endeavor) using a low background holder made of Si material. Measurements were taken at 2θ=10-90 intervals of 0.014 degrees, with FDS 0.3 deg and anti-scatter 3 mm for 0.3 seconds each. The d(002) of the conductive material was obtained by obtaining a graph of the 2θ values ​​measured using XRD, and the peak position of the graph was found by integration, and calculated according to the Bragg law using the following formula 3.

[0080] d(002)=λ / 2sinθ [Formula 3]

[0081] *DoG (Degree of Graphitization): An index used to determine which material the crystal plane of a sample is closest to, between the ideal crystal plane spacing of graphite (3.354 Å) and the crystal plane spacing of coal (3.440 Å). The DoG value is calculated using the following formula 4.

[0082] DoG = (3.440-d(002)) / (3.440-3.354) x 100 [Formula 4]

[0083] *△DoG: DoG after graphitization - DoG before graphitization

[0084] Experimental example (performance evaluation of composite positive electrode) The mixed powder obtained from the examples and comparative examples was pressed into particles using a pressing tool with a specific diameter. The particles were transferred to a pressing tool cell, and 200 mg of sulfide-based all-solid electrolyte powder was placed on the particles, and a pressure of 400 MPa was applied for 60 seconds to form an electrolyte membrane. Then, a Li metal anode was placed face-to-face, and a pressure of 100 MPa was applied for 10 seconds to increase the contact between the electrolyte membrane and the anode. Then, the pressing tool cell was fastened, and the rate characteristics were observed using a charge / discharge device.

[0085] To explain this again, all-solid-state batteries including the positive electrodes produced in the Examples and Comparative Examples were charged and discharged, and the charge capacity (mAh / g), discharge capacity (mAh / g) and capacity retention rate (%) in the first cycle were measured and shown in the following Table 3. Meanwhile, when evaluating the battery performance, the test was performed at a temperature of 60° C. under the following charge and discharge conditions, and ended in a discharged state (a state in which lithium was not present in the negative electrode) (primary charge and discharge test).

[0086] Charging conditions: 0.05C, 4.25V CC / CV, 0.01C cut-off Discharge conditions: 0.05C, 3V CC After the primary charge / discharge test, a secondary charge / discharge test was conducted in which the battery was charged under the same conditions as the primary charge / discharge test, but discharged at 0.5C and 3V CC to measure the capacity retention rate (%). After the secondary charge / discharge test, a tertiary charge / discharge test was conducted in which the battery was charged under the same conditions as the primary charge / discharge test, but discharged at 1C and 3V CC to measure the capacity retention rate (%). The results of the secondary and tertiary charge / discharge tests are also shown in Table 3 and Figure 1 below.

[0087] [Table 3]

[0088] According to Table 3, the batteries using the exemplary conductive materials 1 to 3 having specific properties as fibrous carbon-based conductive materials exhibited better capacity retention than the batteries using the comparative conductive materials 1 to 3 having different properties as particulate carbon-based conductive materials. In addition, the difference in capacity retention became larger as the discharge rate increased, as in the second and third charge-discharge tests. The batteries using the exemplary conductive materials 1 to 3 had excellent rate characteristics, with no significant decrease in capacity retention even at high rates.

[0089] In addition, among fibrous carbon-based conductive materials, graphitization has led to the development of I D / I G It was confirmed that when a conductive material with a change in the value of or DoG value larger than a certain level is used, such as the example conductive material 1, it has better rate characteristics.

[0090] Any simple modifications or variations of the present invention are within the scope of the present invention, and the specific scope of protection of the present invention will be made clear by the appended claims.

Claims

1. The positive electrode active material includes a carbon-based conductive material and an inorganic solid electrolyte. The carbon-based conductive material is a fibrous carbon-based conductive material having a length of 1 μm to 100 μm.

2. 2. The positive electrode for an all-solid-state battery according to claim 1, wherein the carbon-based conductive material is a fibrous carbon-based conductive material having a diameter of 50 nm to 500 nm.

3. The BET specific surface area of ​​the carbon-based conductive material is 1 m ２ / g to 20m ２ The positive electrode for an all-solid-state battery according to claim 1 , wherein the total mass of the positive electrode is 100 wt % or more.

4. 2. The positive electrode for an all-solid-state battery according to claim 1, wherein the powder resistivity of the carbon-based conductive material is 0.025 Ω·cm or less under a pressure of 196 MPa.

5. The density of the carbon-based conductive material is 1 g / cm ３ ~5g / cm ３ The positive electrode for an all-solid-state battery according to claim 1 ,

6. The carbon-based conductive material has an A value of 100 to 500; The positive electrode for an all-solid-state battery according to claim 1, wherein the A value is calculated by the following Equation 1: A = specific surface area x length x density [Formula 1] Here, the specific surface area is the BET specific surface area (m ２ / g), length is the length of the conductive material (μm), and density is the density of the conductive material (g / cm ３ ).

7. The carbon-based conductor material was analyzed by Raman spectroscopy to determine the I Ｄ / I Ｇ The positive electrode for an all-solid-state battery according to claim 1 , wherein the difference in the value of is 0.3 to 0.

7.

8. 2. The positive electrode for an all-solid-state battery according to claim 1, wherein the carbon-based conductive material has a degree of graphitization (DoG) value difference between before and after graphitization of 10 to 50 as determined by XRD analysis.

9. the positive electrode has a B value of 5 to 50; The positive electrode for an all-solid-state battery according to claim 6, wherein the B value is calculated by the following Equation 2: B = R x A [Formula 2] Here, R is a value obtained by dividing the weight of the conductive material by the weight of the positive electrode active material based on the positive electrode, and A is a value calculated according to Equation 1.

10. The positive electrode active material is LiCoO ２ , LiNiO ２ , LiMnO ２ , Li ２ MnO ３ , LiMn ２ O ４ , Li(Ni ａ Co ｂ Mn ｃ ) O ２ (0<a<1, 0<b<1, 0<c<1, a+b+c=1), LiNi １－ｙ Co ｙ O ２ (O<y<1), LiCo １－ｙ Mn ｙ O ２ (O<y<1), LiNi １－ｙ Mn ｙ O ２ (O<y<1), Li(Ni ａ Co ｂ Mn ｃ ) O ４ (0<a<2, 0<b<2, 0<c<2, a+b+c=2), LiMn ２－ｚ Ni ｚ O ４ (0<z<2), LiMn ２－ｚ Co ｚ O ４ The positive electrode for an all-solid-state battery according to any one of claims 1 to 9, wherein z is selected from the group consisting of (0<z<2) and combinations thereof.

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