Conductive material for all-solid-state rechargeable battery, positive electrode for all-solid-state rechargeable battery, and all-solid-state rechargeable battery

Abstract

The present invention relates to a conductive material for an all-solid-state rechargeable battery, a positive electrode for an all-solid-state rechargeable battery, and an all-solid-state rechargeable battery, wherein the conductive material comprises a carbon material; and a coating layer disposed on the surface of the carbon material and containing lithium boron oxide.

Description

Conductive material for all-solid-state secondary batteries, cathode for all-solid-state secondary batteries, and all-solid-state secondary batteries

[0001] This invention relates to a conductive material for an all-solid-state secondary battery, a cathode for an all-solid-state secondary battery, and an all-solid-state secondary battery.

[0002] Lithium-ion batteries, which offer high energy density and portability, are primarily used as the power source for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, active research is being conducted to utilize high-energy-density lithium-ion batteries as power sources for driving or energy storage in hybrid and electric vehicles.

[0003] Since commercially available lithium-ion batteries use electrolytes containing flammable organic solvents, there are safety issues where the battery may explode or catch fire in the event of collisions or penetrations.

[0004] Accordingly, all-solid-state secondary batteries utilizing solid electrolytes instead of liquid electrolytes are being proposed. All-solid-state secondary batteries are composed entirely of solid materials; they offer the advantages of safety by eliminating risks such as explosions caused by electrolyte leakage, and facilitate the fabrication of thin batteries. Furthermore, the reduction in negative electrode thickness enables improved high-speed charging and discharging performance, as well as the realization of high-voltage operation and high energy density.

[0005] In one embodiment, the present invention aims to provide a conductive material for an all-solid-state secondary battery, a cathode for an all-solid-state secondary battery, and an all-solid-state secondary battery that can suppress side reactions with a solid electrolyte and improve ionic conductivity and electrical conductivity.

[0006] One embodiment provides a conductive material for an all-solid-state secondary battery comprising: a carbon material; and a coating layer located on the surface of the carbon material and comprising lithium boron oxide.

[0007] Another embodiment provides a positive electrode for an all-solid-state secondary battery comprising: a positive current collector; and a positive active material layer positioned on the positive current collector and comprising a positive active material, the aforementioned conductive material for an all-solid-state secondary battery, and a binder.

[0008] Another embodiment provides an all-solid-state secondary battery comprising: a positive electrode for the all-solid-state secondary battery described above; a negative electrode; and a solid electrolyte layer located between the positive electrode and the negative electrode.

[0009] According to one embodiment, a conductive material for an all-solid-state secondary battery, a cathode for an all-solid-state secondary battery, and an all-solid-state secondary battery can be provided, which can suppress side reactions with a solid electrolyte and improve ionic conductivity and electrical conductivity.

[0010] FIGS. 1 to 3 are cross-sectional views schematically illustrating an all-solid-state secondary battery according to one embodiment.

[0011] Figure 4 shows the results of electrochemical impedance spectroscopy (EIS) measurements for the all-solid-state secondary batteries prepared in Example 2, Comparative Example 1, and Comparative Example 2.

[0012] Figure 5 is a transmission electron microscope (TEM) image of the conductive material prepared in Example 1.

[0013] Figure 6 shows the results of measuring the initial charge / discharge capacity for the all-solid-state secondary batteries prepared in Example 2, Comparative Example 1, and Comparative Example 2.

[0014] Figure 7 shows the results of measuring the discharge capacity according to 50 cycles for the all-solid-state secondary batteries prepared in Example 2, Comparative Example 1, and Comparative Example 2.

[0015] Figure 8 shows the results of measuring the capacity retention rate according to 50 cycles for the all-solid-state secondary batteries prepared in Example 2, Comparative Example 1, and Comparative Example 2.

[0016] Specific embodiments are described below in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0017] The terms used herein are for describing exemplary embodiments only and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0018] Here, "combinations of these" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, etc.

[0019] The terms "include," "equip," or "have" used herein are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0020] In the drawings, thicknesses have been enlarged to clearly represent various layers and regions, and the same reference numerals have been used for similar parts throughout the specification. When a part such as a layer, film, region, or plate is described as being "on" or "on" another part, this includes not only cases where it is "immediately on" another part, but also cases where there is another part in between. Conversely, when a part is described as being "immediately on" another part, it means that there is no other part in between.

[0021] In addition, the term “layer” here includes not only shapes formed on the entire surface when viewed in a plan view, but also shapes formed on some surfaces.

[0022] The average particle size can be measured by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer, or by using transmission electron microscope or scanning electron microscope images. Alternatively, the average particle size value can be obtained by measuring using dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this. Unless otherwise defined, the average particle size is the diameter (D) of the particle at which the cumulative volume in the particle size distribution is 50 volume%. 50 It may mean ). In addition, unless otherwise defined, the average particle size is obtained by measuring the size (diameter or length of the major axis) of approximately 20 randomly selected particles from scanning electron microscope images to obtain a particle size distribution, and the diameter (D) of the particle with a cumulative volume of 50% in the said particle size distribution. 50 It may be that ) was taken as the average particle size.

[0023] Here, “or” is not interpreted in an exclusive sense; for example, “A or B” is interpreted to include A, B, A+B, etc.

[0024] The term “metal” is interpreted as a concept that includes ordinary metals, transition metals, and metalloids (semimetals).

[0025] Conductive material for all-solid-state secondary batteries

[0026] One embodiment provides a conductive material for an all-solid-state secondary battery comprising: a carbon material; and a coating layer located on the surface of the carbon material and comprising lithium boron oxide.

[0027] All-solid-state secondary batteries are attracting attention as next-generation energy storage devices capable of replacing lithium-ion batteries due to their excellent stability and energy density, and research is particularly being conducted on sulfide-based all-solid-state secondary batteries that possess high lithium-ion conductivity.

[0028] However, compared to the electrolyte of conventional lithium-ion batteries, all-solid-state secondary batteries have a limitation in that the ion conductivity is relatively low because the solid electrolyte cannot cover the entire positive or negative active material.

[0029] Accordingly, composite electrodes are manufactured by mixing solid electrolytes and electrode active materials; however, there is a problem in that electrical conductivity decreases somewhat when the solid electrolyte content increases. Furthermore, in all-solid-state secondary batteries, carbon-based conductive materials can cause adverse reactions with sulfide-based solid electrolytes, leading to a reduction in battery capacity, and this issue raises concerns about the deterioration of the long-term reliability of all-solid-state secondary batteries.

[0030] Accordingly, in one embodiment, we propose a conductive material for an all-solid-state secondary battery that can solve the aforementioned problems, suppress side reactions with a solid electrolyte, and improve ionic conductivity and electrical conductivity.

[0031] A conductive material for an all-solid-state secondary battery according to one embodiment includes a carbon material. Any carbon material used in the relevant technical field may be used as the carbon material, and for example, the carbon material may include natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon nanofiber, carbon nanotube, carbon nanowire, or a combination thereof.

[0032] For example, the carbon material may have an aspect ratio of 2 or more, 2 to 30000, 5 to 25000, 20 to 20000, or 50 to 20000, and for example, the carbon material may include carbon nanofibers, carbon nanotubes, carbon nanowires, or a combination thereof. By using a carbon material with a large aspect ratio to satisfy this, it may be advantageous to improve electrical conductivity by connecting the components constituting the all-solid-state secondary battery. In this case, the aspect ratio of the carbon material may refer to the ratio of the length to the cross-sectional diameter of the carbon material.

[0033] For example, the cross-sectional diameter of the carbon material having an aspect ratio of 2 or more may be 1 nm to 300 nm, 2 nm to 250 nm, 5 nm to 230 nm, or 10 nm to 200 nm, and the length of the carbon material having an aspect ratio of 2 or more may be 1 μm to 300 μm, 5 μm to 250 μm, 10 μm to 250 μm, or 10 μm to 200 μm. When these conditions are met, the conductive material can be used in an all-solid-state secondary battery to improve connectivity between other components within the all-solid-state secondary battery, thereby effectively improving ionic conductivity and electrical conductivity.

[0034] A conductive material according to one embodiment includes a coating layer located on the surface of the carbon material, and the coating layer includes lithium boron oxide. By introducing a coating layer containing lithium boron oxide on the surface of the carbon material, side reactions between the conductive material and the solid electrolyte can be suppressed, and ionic conductivity and electrical conductivity can be improved.

[0035] Methods for coating the surface of a carbon material having an aspect ratio of 2 or more with the lithium boron oxide may include, for example, evaporation, immersion, spraying, atomic deposition, and dry coating methods, but are not limited thereto. As an example, the conductive material may be manufactured using a dry coating method, for instance, by dry mixing the carbon material having an aspect ratio of 2 or more, a lithium-based raw material, and a boron oxide-based raw material, and then heat-treating at a temperature of 300°C to 450°C. When the above heat treatment temperature range is satisfied, the coating material does not penetrate into the interior of the carbon material and is uniformly positioned on the surface of the carbon material to form a good coating layer. Here, the lithium raw material may include lithium hydroxide (LiOH), etc., and the boron oxide raw material may include boric acid (H3BO3), etc.

[0036] For example, the lithium boron oxide is LiBO2, LiB3O5, LiB5O8, Li2B2O4, Li2B2O7, Li2B4O7, Li2B6O7, Li2B6O 10 , Li2B8O 13 , Li3BO3, Li3B7O 12 , Li4B2O5, Li4B 10 O 17 It may include Li6B4O9, or a combination thereof, and a representative example may be Li3BO3. When this is satisfied, not only can side reactions between the conductive material and the solid electrolyte be effectively suppressed, but the conductivity of the conductive material itself can also be improved, thereby enhancing the rate characteristics, charge / discharge characteristics, and lifespan characteristics of the all-solid-state secondary battery using it. In addition, compared to other coating materials, it does not decompose even under high voltage conditions and can form a coating layer well, so it can sufficiently perform the role of a buffer layer, thereby securing excellent conductivity characteristics.

[0037] For example, as the coating layer, the lithium boron oxide may exist on the surface of the conductive material in the form of particles, islands, or films, and the thickness of the coating layer may be 1 nm to 50 nm, 2 nm to 40 nm, 3 nm to 30 nm, or 5 nm to 20 nm. Within this range, it can effectively contribute to securing the effects of suppressing side reactions and improving conductivity without hindering the role of the carbon material.

[0038] For example, the lithium boron oxide may be included in an amount of 0.01 to 5 molar parts, 0.05 to 3 molar parts, 0.1 to 2 molar parts, or 0.3 to 0.8 molar parts relative to 100 molar parts of the carbon material. Within this range, the effects of securing conductivity by the carbon material and suppressing side reactions and improving conductivity by the coating layer can be harmonized.

[0039] anode

[0040] One embodiment provides a positive electrode for an all-solid-state secondary battery comprising: a positive current collector; and a positive active material layer positioned on the positive current collector and comprising a positive active material, the aforementioned conductive material for an all-solid-state secondary battery, and a binder.

[0041] The positive active material layer of the positive electrode according to one embodiment comprises a positive active material, the aforementioned conductive material, and a binder, and may further comprise a solid electrolyte.

[0042] positive electrode active material

[0043] The above-mentioned positive electrode active material may be applied without limitation as long as it is commonly used in all-solid-state secondary batteries, for example, a compound capable of reversible intercalation and deintercalation of lithium may be used, may include a lithium transition metal complex oxide, and may include a compound represented by any one of the following chemical formulas. a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni b Co c L 1 d G eO2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0≤e≤0.1); Li a NiG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn2G b O4(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5); Li (3-f) Fe2(PO4)3(0≤f≤2); Li a FePO4(0.90≤a≤1.8).

[0044] The above-mentioned positive electrode active material may include, for example, lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium nickel cobalt oxide (NC), lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium nickel manganese oxide (NM), lithium manganese oxide (LMO), lithium iron phosphate oxide (LFP), or a combination thereof.

[0045] The above positive active material may include, for example, a lithium nickel-based oxide represented by the following chemical formula 1A, a lithium cobalt-based oxide represented by the following chemical formula 2A, a lithium iron phosphate-based compound represented by the following chemical formula 3A, a cobalt-free lithium nickel-manganese-based oxide represented by the chemical formula 4A, or a combination thereof.

[0046] [Chemical Formula 1A]

[0047] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0048] In the above chemical formula 1A, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, 0≤z1≤0.7, 0.9≤x1+y1+z1≤1.1, and 0≤b1≤0.1, and M 1 and M 2 Each is independently Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zr, or a combination thereof, and X is F, P, S, or a combination thereof.

[0049] In the above chemical formula 1A, 0.6≤x1≤1, 0≤y1≤0.4, and 0≤z1≤0.4, or 0.8≤x1≤1, 0≤y1≤0.2, and 0≤z1≤0.2.

[0050] [Chemical Formula 2A]

[0051] Li a2 Co x2 M 3 y2 O 2-b2 X b2

[0052] In the above chemical formula 2A, 0.9≤a2≤1.8, 0.7≤x2≤1, 0≤y2≤0.3, 0.9≤x2+y2≤1.1, and 0≤b2≤0.1, and M 3 is Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof, and X is F, P, S, or a combination thereof.

[0053] [Chemical Formula 3A]

[0054] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3

[0055] In the above chemical formula 3A, 0.9≤a3≤1.8, 0.6≤x3≤1, 0≤y3≤0.4, and 0≤b3≤0.1, and M4 is Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof, and X is F, P, S, or a combination thereof.

[0056] [Chemical Formula 4A]

[0057] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4

[0058] In the above chemical formula 4A, 0.9≤a2≤1.8, 0.8≤x4<1, 0 <y4≤0.2, 0≤z4≤0.2, 0.9≤x4+y4+z4≤1.1, 및 0≤b4≤0.1이고 M 5 is Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zr, or a combination thereof, and X is F, P, S, or a combination thereof.

[0059] The above positive active material may be in the form of particles, and the average particle size (D) of the above positive active material 50 ) may be 1 μm to 25 μm, for example, 3 μm to 25 μm, 1 μm to 20 μm, 1 μm to 18 μm, 3 μm to 15 μm, or 5 μm to 15 μm. As an example, the anode active material has an average particle size (D 50 Fine particles with a diameter of 1 μm to 9 μm and an average particle size (D 50It may include atoms having a particle size range of 10 μm to 25 μm. A positive electrode active material having this particle size range can be harmoniously mixed with other components within the positive electrode active material layer and can achieve high capacity and high energy density. Here, the average particle size is determined by selecting approximately 20 arbitrary particles from a scanning electron microscope image of the positive electrode active material, measuring their particle sizes (diameter, major axis, or length of the major axis), obtaining a particle size distribution, and determining the diameter (D) of the particle whose cumulative volume is 50 volume% in the particle size distribution. 50 It may be that ) was taken as the average particle size.

[0060] The above positive active material may be in the form of secondary particles formed by the aggregation of a plurality of primary particles, or in the form of single particles. In addition, the above positive active material may be spherical or have a shape close to spherical, or may be polyhedral or irregular in shape.

[0061] Meanwhile, the above-mentioned positive electrode active material may include a buffer layer on the particle surface. The buffer layer may be described as a coating layer, a protective layer, etc., and may serve to lower the interfacial resistance between the positive electrode active material and the solid electrolyte particles. As an example, the buffer layer may include a lithium metal oxide, wherein the metal may be, for instance, Al, B, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ta, V, W, Zr, or a combination thereof. The lithium metal oxide is excellent at lowering the interfacial resistance between the positive electrode active material and the solid electrolyte particles while improving the performance of the positive electrode active material by facilitating the movement of lithium ions and electron conduction.

[0062] bookbinder

[0063] The above binder serves to adhere the positive active material particles well to each other and also to adhere the positive active material well to the positive current collector. Representative examples include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0064] Challenge

[0065] The above positive active material layer may further include a conductive material. The conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon nanofibers, carbon nanotubes, carbon nanowires, etc.; metal-based materials containing copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fibers; conductive polymers such as polyphenylene derivatives; or conductive materials comprising a mixture thereof.

[0066] Aluminum foil may be used as the anode current collector, but is not limited thereto.

[0067] solid electrolyte

[0068] The above solid electrolyte may be an inorganic solid electrolyte and may include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, or a combination thereof.

[0069] Sulfide-based solid electrolytes

[0070] In one embodiment, the solid electrolyte may be a sulfide-based solid electrolyte with excellent ion conductivity. The sulfide-based solid electrolyte particles are, for example, Li2S-P2S5, Li2S-P2S5-LiX (where X is a halogen element, for example, I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p, q are integers, and M is P, Si, Ge, B, Al, Ga or In), or may include a combination thereof.

[0071] Such sulfide-based solid electrolytes can be obtained, for example, by mixing Li2S and P2S5 in a molar ratio of 50:50 to 90:10 or 50:50 to 80:20 and optionally heat-treating. Within the above mixing ratio range, a sulfide-based solid electrolyte having excellent ionic conductivity can be manufactured. Additionally, ionic conductivity may be further improved by including other components such as SiS2, GeS2, B2S3, etc.

[0072] Mechanical milling or the solution method can be applied as mixing methods for sulfur-containing raw materials to manufacture sulfide-based solid electrolytes. Mechanical milling is a method in which starting materials are placed in a ball mill reactor and vigorously stirred to finely atomize and mix them. When using the solution method, starting materials are mixed in a solvent to obtain a solid electrolyte as a precipitate. Furthermore, if heat treatment is performed after mixing, the crystals of the solid electrolyte can become more robust and the ionic conductivity can be improved. For example, a sulfide-based solid electrolyte can be manufactured by mixing sulfur-containing raw materials and heat-treating them two or more times; in this case, a robust sulfide-based solid electrolyte with high ionic conductivity can be produced.

[0073] Sulfide-based solid electrolyte particles according to one embodiment can be manufactured, for example, by mixing sulfur-containing raw materials and calcining at 120°C to 350°C in a first heat treatment, and by mixing the results of the first heat treatment and calcining at 350°C to 800°C in a second heat treatment. The first heat treatment and the second heat treatment can each be carried out in an inert gas or nitrogen atmosphere. The first heat treatment can be performed for 1 to 10 hours, and the second heat treatment can be performed for 5 to 20 hours. Through the first heat treatment, the effect of milling small raw materials can be obtained, and through the second heat treatment, the final solid electrolyte can be synthesized. Through two or more such heat treatments, a high-performance sulfide-based solid electrolyte with high ion conductivity and robustness can be obtained, and such a solid electrolyte can be considered suitable for mass production. The temperature of the first heat treatment may be, for example, 150°C to 330°C or 200°C to 300°C, and the temperature of the second heat treatment may be, for example, 380°C to 700°C or 400°C to 600°C.

[0074] For example, the above sulfide-based solid electrolyte may include an argyrodite-type sulfide. The argyrodite-type sulfide-based solid electrolyte has an ionic conductivity of 10 at room temperature, which is the ionic conductivity of a typical liquid electrolyte. -4 to 10 -2 It has high ionic conductivity close to the S / cm range and can form a tight bond between the positive active material and the solid electrolyte without causing a decrease in ionic conductivity, and furthermore, can form a tight interface between the electrode layer and the solid electrolyte layer. An all-solid-state secondary battery including this can improve battery performance such as rate characteristics, Coulomb efficiency, and life characteristics.

[0075] Azirodite-type sulfides may include, for example, compounds represented by the following chemical formula 1.

[0076] [Chemical Formula 1]

[0077] (Li a M 1 b M 2 c )(P d M 3 e )(S f M 4 g )X h

[0078] In the above chemical formula 1, 4≤a≤8, and M 1 is Mg, Cu, Ag, or a combination thereof, 0≤b<0.5, and M 2 is Na, K, or a combination thereof, 0≤c<0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, and 0 <d<4, 0≤e<1 이고, M 4 is O, SO n , or a combination thereof, 1.5≤n≤5, 3≤f≤12, 0≤g<2, X is F, Cl, Br, I, or a combination thereof, and 0≤h≤2.

[0079] For example, in Chemical Formula 1, a halide element (X) may be necessarily included, in which case 0 <h≤2로 표시될 수 있다. 일 예로 화학식 1에 M 1 An element may be required, in which case 0 <b<0.5로 표시될 수 있다. 화학식 1에서 M 3 can be understood as an element substituted in the P position, and 0 <e<1일 수 있다. 화학식 1에서 M 4 is substituted in the S position, for example, 0 <g<2일 수 있으며 S의 비율인 f는 예를 들어 3≤f≤7일 수 있다. M 4 ga SO n In the case of SO n It can be, for example, S4O6, S3O6, S2O3, S2O4, S2O5, S2O6, S2O7, S2O8, SO4, or SO5, and as an example, it can be SO4.

[0080] For example, in Chemical Formula 1, a+b+c+h=7, d+e=1, and f+g+h=6.

[0081] As a specific example, azirodite-type sulfides include Li3PS4 and Li7P3S 11 , Li7PS6, Li6PS5Cl, Li6PS5Br, Li 5.8 PS 4.8 Cl 1.2 , Li 6.2 PS 5.2 Br 0.8 , Li 5.75 PS 4.75 Cl 1.25 , (Li 5.69 Cu 0.06 )PS 4.75 Cl 1.25 , (Li 5.72 Cu 0.03 )PS 4.75 Cl 1.25 , (Li 5.69 Cu 0.06 )P(S 4.70 (SO4) 0.05 )Cl 1.25 , (Li 5.69 Cu 0.06 )P(S 4.60(SO4) 0.15 )Cl 1.25 , (Li 5.72 Cu 0.03 )P(S 4.725 (SO4) 0.025 )Cl 1.25 , (Li 5.72 Na 0.03 )P(S 4.725 (SO4) 0.025 )Cl 1.25 , Li 5.75 P(S 4.725 (SO4) 0.025 )Cl 1.25 , or a combination thereof may be included, but is not limited thereto.

[0082] An azirodite-type sulfide-based solid electrolyte can be prepared by mixing, for example, lithium sulfide and phosphorus sulfide, and optionally lithium halide. After mixing these, heat treatment may be performed. The heat treatment may include, for example, two or more heat treatment steps. Here, preparing an azirodite-type sulfide-based solid electrolyte may include, for example, a first heat treatment in which raw materials are mixed and calcined at 120°C to 350°C, and a second heat treatment in which the result of the first heat treatment is mixed again and calcined at 350°C to 800°C.

[0083] Sulfide-based solid electrolytes can be in the form of particles, and the average particle size (D) of the sulfide-based solid electrolyte particles 50 ) may, for example, be 0.1 μm to 5.0 μm or 0.1 μm to 3.0 μm, and may be fine particles of 0.1 μm to 1.9 μm or coarse particles of 2.0 μm to 5.0 μm. The sulfide-based solid electrolyte particles may be a mixture of fine particles with an average particle size of 0.1 μm to 1.9 μm and coarse particles with an average particle size of 2.0 μm to 5.0 μm. The average particle size of the sulfide-based solid electrolyte particles may be measured using electron microscope images, for example, by measuring the size (diameter or length of the major axis) of about 20 particles from scanning electron microscope images to obtain a particle size distribution, where D50 It could be that it was calculated.

[0084] oxide-based solid electrolytes

[0085] The positive active material layer may include an oxide-based solid electrolyte as a solid electrolyte. The oxide-based inorganic solid electrolyte is, for example, Li 1+x Ti 2-x Al(PO4)3(LTAP)(0≤x≤4), 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, Lithium Phosphate (Li3PO4), Lithium Titanium Phosphate (Li x Ti y (PO4)3, 0 <x<2, 0<y<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), lithium lanthanum titanate(Li x La y TiO3, 0 <x<2, 0<y<3), Li2O, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2계 세라믹스, 가넷(Garnet)계 세라믹스 Li 3+x La3M2O 12 (M= Te, Nb, or Zr; x is an integer from 1 to 10), or may include a mixture thereof.

[0086] Halide-based solid electrolytes

[0087] The positive active material layer is a solid electrolyte and may include a halide-based solid electrolyte. The halide-based solid electrolyte contains a halogen element as a main component, and the ratio of the halogen element to all elements constituting the solid electrolyte may be 50 mol% or more, 70 mol% or more, 90 mol% or more, or 100 mol%. As an example, the halide-based solid electrolyte may not contain a sulfur element.

[0088] The halide-based solid electrolyte may contain a lithium element, a metal element other than lithium, and a halogen element. The metal element other than lithium may be Al, As, B, Bi, Ca, Cd, Co, Cr, Fe, Ga, Hf, In, Mg, Mn, Ni, Sb, Sc, Sn, Ta, Ti, Y, Zn, Zr, or a combination thereof. The halogen element may be F, Cl, Br, I, or a combination thereof, and for example, may be Cl, Br, or a combination thereof. The halide-based solid electrolyte is, for example, Li a It can be represented as M1X6 (M is Al, As, B, Bi, Ca, Cd, Co, Cr, Fe, Ga, Hf, In, Mg, Mn, Ni, Sb, Sc, Sn, Ta, Ti, Y, Zn, Zr, or a combination thereof, X is F, Cl, Br, I, or a combination thereof, and 2≤a≤3). The above halide-based solid electrolyte is, for example, Li2ZrCl6, Li 2.7 Y 0.7 Zr 0.3 Cl6, Li 2.5 Y 0.5 Zr 0.5 Cl6, Li 2.5 In 0.5 Zr 0.5 Cl6, Li2In 0.5 Zr 0.5 Cl6, Li3YBr6, Li3YCl6, Li3YBr2Cl4, Li3YbCl6, Li 2.6Hf 0.4 Yb 0.6 It may include Cl6, or a combination thereof, but is not limited thereto.

[0089] Solid electrolytes can be in the form of particles, and the average particle size (D) of the solid electrolyte particles 50 The ) may be 5.0 μm or less, for example, 0.1 μm to 5.0 μm, 0.5 μm to 5.0 μm, 0.5 μm to 4.0 μm, 0.5 μm to 3.0 μm, 0.5 μm to 2.0 μm, or 0.5 μm to 1.0 μm. Such a solid electrolyte can effectively penetrate between the positive electrode active materials, and has excellent contact with the positive electrode active materials and connectivity between the solid electrolyte particles.

[0090] For example, the positive active material layer may contain the positive active material in an amount of 55% to 99.7%, 58% to 98.6%, 66% to 94.3%, 71.7% to 91.1%, or 77.4% to 88.9%, relative to 100% by weight of the positive active material layer.

[0091] For example, the positive active material layer may include the conductive material in an amount of 0.1% to 5%, 0.1% to 3%, 0.2% to 1%, 0.3% to 0.8%, or 0.3% to 0.6% relative to 100% by weight of the positive active material layer.

[0092] For example, the positive active material layer may contain the binder in an amount of 0.1% to 5% by weight, 0.3% to 4% by weight, 0.5% to 3% by weight, 0.6% to 2.5% by weight, or 0.8% to 2% by weight relative to 100% by weight of the positive active material layer.

[0093] For example, the positive active material layer may contain the solid electrolyte in an amount of 0.1% to 35%, 1% to 35%, 5% to 30%, 8% to 25%, or 10% to 20% with respect to 100% by weight of the positive active material layer.

[0094] All-solid-state secondary battery

[0095] In one embodiment, an all-solid-state secondary battery is provided, comprising: a positive electrode for the all-solid-state secondary battery described above; a negative electrode; and a solid electrolyte layer located between the positive electrode and the negative electrode.

[0096] FIG. 1 is a cross-sectional view of an all-solid-state secondary battery according to one embodiment. Referring to FIG. 1, the all-solid-state secondary battery (100) may have a structure in which an electrode assembly is housed in a battery case, wherein the electrode assembly comprises a negative electrode (400) including a negative electrode current collector (401) and a negative electrode active material layer (403), a solid electrolyte layer (300), and a positive electrode (200) including a positive electrode active material layer (203) and a positive electrode current collector (201). The all-solid-state secondary battery (100) may further include an elastic layer (500) on the outer side of at least one of the positive electrode (200) and the negative electrode (400). FIG. 1 illustrates a unit cell comprising a cathode (400), a solid electrolyte layer (300), and a positive electrode (200). However, as illustrated in FIG. 3, a solid-state secondary battery may be manufactured by stacking two or more unit cells, or by stacking two or more unit cells, for example, 2 to 100, 3 to 50, 4 to 20, etc. Additionally, the unit cell may include one or more cathodes, and likewise may include one or more solid electrolyte layers and one or more positive electrodes. For example, the unit cell may be a monocell with a positive electrode / solid electrolyte layer / cathode structure, or a bicell with a negative electrode / solid electrolyte layer / positive electrode / solid electrolyte layer / cathode structure.

[0097] cathode

[0098] A negative electrode for an all-solid-state secondary battery comprises, for example, a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material and may further comprise a binder and / or a conductive material.

[0099] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0100] A material capable of reversibly intercalating / deintercalating the above lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0101] As the above lithium metal alloy, an alloy of a metal selected from the group consisting of lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0102] As a material capable of doping and undoping the above lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used, and the Si-based negative electrode active material may include silicon, a silicon-carbon composite, or SiO₂. x(0 <x≤2), Si-Q 합금(상기 Q는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님), 상기 Sn계 음극 활물질로는 Sn, SnO2, Sn-R 합금(상기 R은 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Sn은 아님) 등을 들 수 있고, 또한 이들 중 적어도 하나와 SiO2를 혼합하여 사용할 수도 있다. 상기 원소 Q 및 R로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, 및 이들의 조합으로 이루어진 군에서 선택되는 것을 사용할 수 있다.

[0103] For example, the negative electrode active material may include silicon-carbon composite particles. The average particle size (D) of the silicon-carbon composite particles 50 ) may be, for example, 0.5 μm to 20 μm. With respect to 100 wt% of the silicon-carbon composite particles, silicon may be included in an amount of 10 wt% to 60 wt% and carbon may be included in an amount of 40 wt% to 90 wt%. The silicon-carbon composite particles may include, for example, a core containing silicon particles and a carbon coating layer located on the surface of the core. The average particle size (D) of the silicon particles in the core 50) may be 10 nm to 1 µm, or 10 nm to 200 nm. The silicon particles may exist as silicon alone, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is SiO x (0 <x≤2)로 표시될 수 있다. 또한, 상기 탄소 코팅층의 두께는 약 5 ㎚ 내지 100 ㎚일 수 있다.

[0104] For example, the silicon-carbon composite particles may comprise a core containing silicon particles and crystalline carbon, and a carbon coating layer located on the surface of the core containing amorphous carbon. For example, in the silicon-carbon composite particles, the amorphous carbon may not be present in the core but only in the carbon coating layer. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof, and the amorphous carbon may be formed from coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or a polymer resin (phenol resin, furan resin, polyimide resin, etc.). In this case, the content of crystalline carbon may be 10% to 70% by weight and the content of amorphous carbon may be 20% to 40% by weight with respect to 100% by weight of the silicon-carbon composite particles.

[0105] In silicon-carbon composite particles, the core may include a void in the central portion. The radius of the void may be 30% to 50% of the radius of the silicon-carbon composite particle.

[0106] Silicon-carbon composite particles effectively suppress problems such as volume expansion, structural collapse, or particle fragmentation due to charging and discharging, thereby preventing the interruption of conductive paths and enabling the realization of high capacity and high efficiency, making them advantageous for use under high voltage or high-speed charging conditions.

[0107] Si-based negative electrode active material or Sn-based negative electrode active material may be used in combination with carbon-based negative electrode active material. When Si-based negative electrode active material or Sn-based negative electrode active material and carbon-based negative electrode active material are mixed and used, the mixing ratio may be 1:99 to 90:10 by weight.

[0108] The content of the negative electrode active material for 100 weight% of the negative electrode active material layer may be 95 weight% to 99 weight%.

[0109] In one embodiment, the negative electrode active material layer further comprises a binder and optionally further comprises a conductive material. The content of the binder may be 1% to 5% by weight with respect to 100% by weight of the negative electrode active material layer. Additionally, when further comprising a conductive material, the negative electrode active material layer may comprise 90% to 98% by weight of the negative electrode active material, 1% to 5% by weight of the binder, and 1% to 5% by weight of the conductive material.

[0110] The binder serves to effectively bond the negative electrode active material particles to each other and also to effectively bond the negative electrode active material to the negative electrode current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

[0111] Examples of water-insoluble binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, ethylene propylene copolymer, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0112] Examples of water-soluble binders include rubber-based binders or polymer resin binders. The rubber-based binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder may be selected from polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0113] When a water-soluble binder is used as the cathode binder, a cellulose-based compound capable of imparting viscosity as a type of thickener may be further included. As this cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K, or Li may be used as the alkali metal. The content of such a thickener may be 0.1 to 3 parts by weight per 100 parts by weight of the cathode active material.

[0114] A conductive material is used to impart conductivity to an electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon nanofibers, carbon nanotubes, and carbon nanowires; metal-based materials in the form of metal powder or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or conductive materials including mixtures thereof.

[0115] As a cathode current collector, a material selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof may be used.

[0116] Alternatively, as another example, the negative electrode for an all-solid-state secondary battery may be a precipitation-type negative electrode, unlike the one described above. The precipitation-type negative electrode may refer to a negative electrode that does not contain a negative electrode active material during battery assembly, but in which lithium metal, etc. is precipitated or electrodeposited on the negative electrode during battery charging, and which acts as the negative electrode active material.

[0117] FIG. 2 is a schematic cross-sectional view of an all-solid-state secondary battery including a precipitation type negative electrode. Referring to FIG. 2, the precipitation type negative electrode (400') may include a negative electrode current collector (401) and a negative electrode coating layer (405) located on the negative electrode current collector. An all-solid-state secondary battery having such a precipitation type negative electrode (400') starts initial charging in a state where no negative electrode active material is present, and during charging, a high-density lithium metal is precipitated or electrodeposited between the negative electrode current collector (401) and the negative electrode coating layer (405), or on the negative electrode coating layer (405), to form a lithium metal layer (404), which can serve as a negative electrode active material. Accordingly, in a solid-state secondary battery that has undergone one or more charges, the precipitation type negative electrode (400') may include, for example, a negative electrode current collector (401), a lithium metal layer (404) located on the negative electrode current collector, and a negative electrode coating layer (405) located on the metal layer. The lithium metal layer (404) refers to a layer in which lithium metal, etc. is precipitated during the charging process of the battery, and may be referred to as a metal layer, a lithium layer, a lithium electrodeposition layer, or a negative electrode active material layer.

[0118] The negative electrode coating layer (405) may be a lithium electrodeposition inducing layer or a negative electrode catalyst layer, and may include a metal, carbon material, or a combination thereof that acts as a catalyst.

[0119] The above metal may be a lithium-friendly metal and may include, for example, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, zinc, or a combination thereof, and may be composed of one of these or may be composed of several types of alloys. When the metal exists in the form of particles, its average particle size (D 50 ) can be about 4 μm or less, and for example, 10 nm to 4 μm.

[0120] The carbon material may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. Crystalline carbon may be, for example, natural graphite, artificial graphite, mesophase carbon micro beads, or a combination thereof. Amorphous carbon may be, for example, carbon black, activated carbon, acetylene black, Denka black, Ketjen black, or a combination thereof.

[0121] When the negative electrode coating layer (405) includes both the metal and the carbon material, the mixing ratio of the metal and the carbon material may be, for example, a weight ratio of 1:10 to 2:1. In this case, the precipitation of lithium metal can be effectively promoted and the characteristics of the all-solid-state secondary battery can be improved. The negative electrode coating layer (405) may include, for example, a carbon material supported with a catalyst metal, or may include a mixture of metal particles and carbon material particles.

[0122] The cathode coating layer (405) may, for example, include the metal and amorphous carbon, and in this case, can effectively promote the precipitation of lithium metal.

[0123] The cathode coating layer (405) may further include a binder, and the binder may be, for example, a conductive binder. In addition, the cathode coating layer (405) may further include general additives such as fillers, dispersants, ion conductive agents, etc.

[0124] The thickness of the cathode coating layer (405) may be, for example, 100 nm to 20 μm, or 500 nm to 10 μm, or 1 μm to 5 μm.

[0125] The precipitation type cathode (400') may, for example, further include a thin film on the surface of the cathode current collector, that is, between the cathode current collector and the cathode coating layer. The thin film may include an element capable of forming an alloy with lithium. The element capable of forming an alloy with lithium may be, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., and may be composed of one of these or composed of several types of alloys. The thin film can further flatten the precipitation shape of the lithium metal layer (404) and further improve the characteristics of the all-solid-state secondary battery. The thin film may be formed by, for example, vacuum deposition, sputtering, plating, etc. The thickness of the thin film may be, for example, 1 nm to 500 nm.

[0126] The lithium metal layer (404) may include lithium metal or a lithium alloy. The lithium alloy may be, for example, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, or a Li-Si alloy.

[0127] The thickness of the lithium metal layer (404) may be 1 µm to 500 µm, 1 µm to 200 µm, 1 µm to 100 µm, or 1 µm to 50 µm. If the thickness of the lithium metal layer (404) is too thin, it is difficult to perform the function of a lithium storage tank, and if it is too thick, the battery volume may increase and performance may deteriorate.

[0128] When such a precipitation type cathode is applied, the cathode coating layer (405) can protect the lithium metal layer (404) and suppress the precipitation growth of lithium deadlite. Accordingly, short circuits and capacity degradation of the all-solid-state battery are suppressed, and lifespan characteristics can be improved.

[0129] solid electrolyte layer

[0130] In an all-solid-state secondary battery according to one embodiment, a solid electrolyte layer (300) is located between a positive electrode (200) and a negative electrode (400), and the solid electrolyte layer (300) includes a solid electrolyte. The solid electrolyte included in the solid electrolyte layer (300) may include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, or a combination thereof. At this time, since the details regarding the sulfide-based solid electrolyte, the oxide-based solid electrolyte, and the halide-based solid electrolyte are as described above, a detailed description is omitted.

[0131] Meanwhile, the average particle size (D) of the solid electrolyte included in the solid electrolyte layer (300) 50 ) is the average particle size (D) of the solid electrolyte contained in the anode (200). 50 It may be larger than ). In this case, overall performance can be improved by increasing the mobility of lithium ions while maximizing the energy density of the all-solid-state secondary battery. For example, the average particle size (D) of the solid electrolyte included in the positive electrode (200) 50 ) may be 0.1 μm to 1.9 μm, or 0.1 μm to 1.0 μm, and the average particle size (D) of the solid electrolyte included in the solid electrolyte layer (300) 50 ) may be 2.0 μm to 5.0 μm, or 2.0 μm to 4.0 μm, or 2.5 μm to 3.5 μm. When such particle size ranges are satisfied, the energy density of the all-solid-state secondary battery is maximized, while lithium ion transport is facilitated to suppress resistance, thereby improving the overall performance of the all-solid-state secondary battery. Here, the average particle size (D) of the solid electrolyte 50 ) may be measured using a particle size analyzer utilizing laser diffraction.

[0132] The solid electrolyte layer (300) may further include a binder in addition to the solid electrolyte. In this case, the binder may be styrene butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, acrylate-based polymer, or a combination thereof, but is not limited thereto, and any material used as a binder in the relevant technical field may be used. The acrylate-based polymer may be, for example, butyl acrylate, polyacrylate, polymethacrylate, or a combination thereof.

[0133] A solid electrolyte layer (300) can be formed by adding a solid electrolyte to a binder solution, coating the solution onto a substrate film, and drying it. The solvent of the binder solution may be octyl acetate, isobutyryl isobutylate, xylene, toluene, benzene, hexane, or a combination thereof. Since the process of forming the solid electrolyte layer is widely known in the field, a detailed description will be omitted.

[0134] The thickness of the solid electrolyte layer (300) can be, for example, 10 μm to 150 μm.

[0135] The solid electrolyte layer (300) may further include an alkali metal salt, and / or an ionic liquid, and / or a conductive polymer.

[0136] The alkali metal salt may be, for example, a lithium salt. The content of the lithium salt in the solid electrolyte layer may be 1 M or more, for example, 1 M to 4 M. In this case, the lithium salt can improve ion conductivity by improving the lithium ion mobility of the solid electrolyte layer.

[0137] Lithium salts may be applied without limitation of type and may include, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiSCN, LiN(CN)2, lithium bis(oxalateto)borate (LiBOB), lithium difluoro(oxalateto)borate (LiDFOB), lithium difluorobis(oxalateto)phosphate (LiDFBP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, or combinations thereof.

[0138] For example, the lithium salt may be an imide-based lithium salt such as LiTFSI, LiFSI, LiBETI, or a combination thereof. Imide-based lithium salts can maintain or improve ionic conductivity by appropriately maintaining chemical reactivity with ionic liquids.

[0139] Ionic liquids are salts or room temperature molten salts that have a melting point below room temperature, are in a liquid state at room temperature, and consist only of ions.

[0140] The ionic liquid comprises 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 - , BF4 -, SO4 - , CF3SO3 - , (FSO2)2N - , (C2F5SO2)2N - , (C2F5SO2)(CF3SO2)N - , and (CF3SO2)2N - It may be a compound containing one or more anions selected from among.

[0141] The ionic liquid may be one or more selected from the group consisting of, for example, N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(3-trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazoliium bis(trifluoromethylsulfonyl)amide, and 1-ethyl-3-methylimidazoliium bis(trifluoromethylsulfonyl)amide.

[0142] The weight ratio of the solid electrolyte to the ionic liquid in the solid electrolyte layer may be 0.1:99.9 to 90:10, and for example, 10:90 to 90:10, 20:80 to 90:10, 30:70 to 90:10, 40:60 to 90:10, or 50:50 to 90:10. A solid electrolyte layer satisfying the above range can maintain or improve ionic conductivity by increasing the electrochemical contact area with the electrode. Accordingly, the energy density, discharge capacity, rate characteristics, etc. of the all-solid-state secondary battery can be improved.

[0143] The all-solid-state secondary battery may be a unit cell having a structure of a positive electrode / solid electrolyte layer / negative electrode, a bicell having a structure of a negative electrode / solid electrolyte layer / positive electrode / solid electrolyte layer / negative electrode, or a stacked battery in which the structure of the unit cell is repeated.

[0144] The shape of the all-solid-state secondary battery is not particularly limited and may be, for example, coin-type, button-type, sheet-type, stacked-type, cylindrical-type, flat-type, etc. In addition, the all-solid-state secondary battery can be applied to large batteries used in electric vehicles, etc. For example, the all-solid-state secondary battery can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). In addition, it can be used in fields requiring a large amount of power storage, for example, in electric bicycles or power tools. Furthermore, the above-mentioned all-solid-state secondary battery can be used in various fields such as portable electronic devices.

[0145] Examples and comparative examples of the present invention are described below. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0146] Example 1

[0147] 1. Manufacture of conductive materials

[0148] Length 10 µm to 200 µm, diameter 10 nm to 200 nm, surface area 300 m² 2 A long-carbon nanotube (LCNT) with a thickness of 20 nm was prepared, and powdered LiOH and H3BO3 were added in a molar ratio of 3:1 at a ratio of 0.5 molar parts per 100 molar parts of LCNT. After uniform dry mixing to coat Li3BO3 on the surface of the CNT, the mixture was calcined at 400 °C to produce a conductive material in the form of an LCNT with a Li3BO3 coating layer having a thickness of 20 nm.

[0149] 2. Manufacture of the anode

[0150] LiNi 0.945 Co 0.04 Al 0.015 85 wt% O2 positive electrode active material, azirodite-type solid electrolyte of Li6PS5Cl (D 50A cathode composition was prepared by adding 13.44 wt% of (=3 μm), 1 wt% of PVdF binder, 0.4 wt% of the conductive material prepared above, and 0.16 wt% of hydrogenated nitrile butadiene rubber (HNBR) as a dispersant to an octyl acetate (OA) solvent and mixing. The composition was applied to a cathode current collector and dried at 80°C to prepare a cathode.

[0151] 3. Preparation of the cathode

[0152] Day 7 carbon black with a particle size of approximately 30 nm and average particle size (D 50 An Ag / C composite was prepared by mixing silver (Ag) with a thickness of approximately 60 nm in a weight ratio of 3:1, and 0.25 g of the composite was added to 2 g of an NMP solution containing 7 wt% of PVdF binder and mixed to prepare a cathode coating layer composition. This was applied onto a cathode current collector and dried to prepare a precipitation type cathode with a cathode coating layer formed on the cathode current collector.

[0153] 4. Preparation of Solid Electrolyte Layer

[0154] An azirodite-type solid electrolyte of Li6PS5Cl was added to an OA solvent containing an acrylic binder and mixed to prepare a composition for forming a solid electrolyte layer. The composition was cast onto a release film and dried at 80°C to prepare a solid electrolyte layer.

[0155] 5. Manufacturing of all-solid-state secondary batteries

[0156] The prepared positive electrode, negative electrode, and solid electrolyte layer were cut, and the solid electrolyte layer was laminated onto the positive electrode, followed by the lamination of the negative electrode. The mixture was sealed in a pouch form and subjected to high-temperature hydrostatic pressing (WIP) at 85°C at 500 MPa for 30 minutes to manufacture an all-solid-state secondary battery.

[0157] Example 2

[0158] A lithium foil is punched into a circular shape with a diameter of 13 mm and used as the negative electrode, and a solid electrolyte (Li6PS5Cl; D 50150 mg (=3㎛) is added in powder form and used as a solid electrolyte layer, and LiNi 0.945 Co 0.04 Al 0.015 O2 positive electrode active material and Li6PS5Cl solid electrolyte (D 50 30 mg of a composite material, uniformly mixed in a weight ratio of 60:35:5 with a conductive material that is an LCNT with a Li3BO3 coating layer prepared in Example 1 (=3㎛), was used as the cathode, and this was combined into a lithium-half (Li-half) torque cell to manufacture an all-solid-state secondary battery. At this time, the combined pressure was about 300 MPa and the measured pressure was about 30 MPa.

[0159] Comparative Example 1

[0160] An all-solid-state secondary battery was manufactured in substantially the same manner as in Example 2, except that, as the conductive material, a conductive material was prepared in which a Li6Zr2O7 coating layer was formed on an LCNT using 2 molar parts of ZrO2 and 6 molar parts of LiOH to coat Li6Zr2O7 on the surface of the LCNT, and this was used.

[0161] Comparative Example 2

[0162] An all-solid-state secondary battery was manufactured in substantially the same manner as in Example 2, except that the uncoated LCNT carbon material itself was used as the conductive material.

[0163] Evaluation Example 1: Evaluation of Conductivity Characteristics

[0164] To evaluate the conductivity characteristics of the conductive material, the all-solid-state secondary batteries prepared in Example 2, Comparative Example 1, and Comparative Example 2 were charged at 4.25 V and 0.1 C-rate in a 45 ℃ environment and measured by electrochemical impedance spectroscopy (EIS), and the results are shown in Fig. 4.

[0165] Referring to FIG. 4, it can be confirmed that the conductivity of Example 2 is superior to that of Comparative Example 1. Accordingly, in the conductive material, which is an LCNT with a Li6Zr2O7 coating layer formed in Comparative Example 1, the lithium zirconium oxide (Li6Zr2O7) included in the coating layer has the property of decomposing at a high voltage of 4.0 V or higher, so it can decompose at high voltage, causing lithium to escape and clump together in the form of zirconium. As a result, the coating layer containing lithium zirconium oxide may have difficulty performing the role of a buffer layer, and it can be presumed that the conductivity is reduced as a result.

[0166] On the other hand, in the conductive material which is an LCNT with a Li3BO3 coating layer formed in Example 2, it can be seen that the lithium boron oxide (Li3BO3) included in the coating layer does not decompose even at a high voltage of 4.0 V or higher, and forms a coating layer well, sufficiently performing the role of a buffer layer to secure excellent conductivity.

[0167] In addition, in the case of Comparative Example 2, it can be confirmed that the conductivity is lower compared to Example 2 by using an uncoated LCNT carbon material as the conductive material. This is because the LCNT conductive material with a Li3BO3 coating layer used in Example 2 has an ion-conducting material coated on the surface of the carbon material compared to the uncoated LCNT conductive material used in Comparative Example 2, making it possible to manufacture an electrode plate with superior ion conductivity. Furthermore, since the uncoated LCNT carbon material used in Comparative Example 2 can degrade by reacting with a sulfide-based solid electrolyte, it can be seen that using an LCNT conductive material with a Li3BO3 coating layer as in Example 2 is advantageous in terms of securing long life characteristics.

[0168] Evaluation Example 2: Coating Performance Evaluation

[0169] Images of the conductive material prepared in Example 1, taken with a transmission electron microscope (TEM), are shown in Figure 5.

[0170] Referring to Fig. 5, in the case of the conductive material prepared in Example 1, a coating layer containing lithium boron oxide is uniformly formed on the surface of the LCNT carbon material, and it can be confirmed that the coating layer covers the surface of the LCNT carbon material well in the conductive material.

[0171] Evaluation Example 3: Evaluation of Initial Charge / Discharge Characteristics

[0172] For the all-solid-state secondary batteries prepared in Example 2, Comparative Example 1, and Comparative Example 2, the initial charge capacity and discharge capacity were measured after charging to an upper limit voltage of 4.25V with a constant current of 0.1C at 45℃ and to a constant voltage of 0.05C, and then discharging to a cutoff voltage of 2.5V with a constant current of 0.1C. Then, the efficiency (%), which is the ratio of the latter to the former, was measured, and the results are shown in FIG. 6 and Table 1 below.

[0173] Initial Charge Capacity (mAh / g) Initial Discharge Capacity (mAh / g) Initial Efficiency (%) Example 2 23 4.76 20 4.45 8 7.09 Comparative Example 1 23 2.53 19 8.02 8 5.16 Comparative Example 2 23 6.85 20 1.39 8 5.03

[0174] Referring to Figure 6 and Table 1, it can be seen that in the case of Example 2, compared to Comparative Example 1 and Comparative Example 2, at least one of the initial charge capacity and initial discharge capacity is higher, and the initial efficiency is excellent.

[0175] Evaluation Example 4: Rate Characteristic Evaluation

[0176] For the all-solid-state secondary batteries prepared in Example 2, Comparative Example 1, and Comparative Example 2, the rate characteristics of the battery were evaluated by charging the battery at 45°C with a constant current of 0.1C to an upper limit voltage of 4.25V and a constant voltage of 0.05C, then discharging it at 0.1C to a cutoff voltage of 2.5V, and then charging the battery in the same process and discharging it at a high rate of 0.33C and 1.0C to a cutoff voltage of 2.5V. Subsequently, the recovery capacity was evaluated by charging it again in the same process and then discharging it at 0.1C to a cutoff voltage of 2.5V.

[0177] Table 2 below shows the discharge capacities of 0.1C, 0.33C, and 1.0C, and the recovery capacity of 0.1C, respectively.

[0178] 0.1C Discharge Capacity (mAh / g) 0.33C Discharge Capacity (mAh / g) 1.0C Discharge Capacity (mAh / g) 0.1C Recovery Capacity (mAh / g) Example 2 205.3 192.1 177.9 198.8 Comparative Example 1 200.4 186.4 166.2 192.12 Comparative Example 2 203.2 189.1 172.6 196.4

[0179] Referring to Table 2, it can be seen that in the case of Example 2, the discharge capacities of 0.1C, 0.33C, and 1.0C, and the recovery capacity of 0.1C are excellent. On the other hand, in the case of Comparative Examples 1 and 2, the discharge capacities of 0.1C, 0.33C, and 1.0C, and the recovery capacity of 0.1C are lower compared to Example 2.

[0180] Evaluation Example 5: Life Characteristics Evaluation

[0181] For the all-solid-state secondary batteries prepared in Example 2, Comparative Example 1, and Comparative Example 2, as in Evaluation Example 4, a charge-discharge cycle was performed by charging at 45°C with a constant current of 0.1C to an upper limit voltage of 4.25V and with a constant voltage of 0.05C, followed by discharging at 0.1C to a cutoff voltage of 2.5V. This process of charging at 0.33C and discharging at 0.33C within a voltage range of 2.5V to 4.25V at 45°C was repeated 50 times. From this, the discharge capacity at the first cycle, the discharge capacity at the 50th cycle, and the 50-cycle capacity retention rate—which is the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the first cycle—were evaluated, and the results are shown in Table 3 below. Additionally, the discharge capacity and capacity retention rate according to 50 cycles for the all-solid-state secondary batteries prepared in Example 2, Comparative Example 1, and Comparative Example 2 are shown in Figures 7 and 8, respectively.

[0182] Initial Discharge Capacity (mAh / g) 50 Cycles Discharge Capacity (mAh / g) 50 Cycles Capacity Retention Rate (%) Example 2 17 5.24 15 7.66 90.0 Comparative Example 1 16 9.94 14 5.88 85.8 Comparative Example 2 17 2.71 15 2.18 88.1

[0183] Referring to Table 3, Figures 7 and 8, it can be seen that Example 2 has a higher initial discharge capacity, 50th discharge capacity, and 50th capacity retention rate compared to Comparative Examples 1 and 2.

[0184] Although preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concepts defined in the following claims are also included within the scope of the present invention.

[0185] [Explanation of the symbol]

[0186] 100: All-solid-state secondary battery 200: Cathode

[0187] 201: Positive current collector 203: Positive active material layer

[0188] 300: Solid electrolyte layer 400: Cathode

[0189] 401: Cathode current collector 403: Cathode active material layer

[0190] 400': Precipitation type cathode 404: Lithium metal layer

[0191] 405: Cathode coating layer 500: Elastic layer

Claims

Carbon material; and A conductive material for an all-solid-state secondary battery comprising a coating layer located on the surface of the carbon material and containing lithium boron oxide. In Article 1, The above carbon material is a conductive material for all-solid-state secondary batteries comprising natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon nanofiber, carbon nanotube, carbon nanowire, or a combination thereof. In Article 1, The above carbon material is a conductive material for an all-solid-state secondary battery having an aspect ratio of 2 or more. In Article 1, The above carbon material is a conductive material for all-solid-state secondary batteries comprising carbon nanofibers, carbon nanotubes, carbon nanowires, or a combination thereof. In Article 1, A conductive material for an all-solid-state secondary battery having a coating layer thickness of 1 nm to 50 nm. In Article 1, A conductive material for an all-solid-state secondary battery comprising 0.01 to 5 molar parts of the lithium boron oxide relative to 100 molar parts of the carbon material. In Article 1, The above lithium boron oxide is a conductive material for an all-solid-state secondary battery that exists in the form of particles, islands, or films on the surface of the conductive material. In Article 1, The above lithium boron oxide is LiBO2, LiB3O5, LiB5O8, Li2B2O4, Li2B2O7, Li2B4O7, Li2B6O7, Li2B6O 10 , Li2B8O 13 , Li3BO3, Li3B7O 12 , Li4B2O5, Li4B 10 O 17 A conductive material for an all-solid-state secondary battery comprising , Li6B4O9, or a combination thereof. In Paragraph 3, A conductive material for an all-solid-state secondary battery having a cross-sectional diameter of 1 nm to 300 nm of the carbon material. In Paragraph 3, A conductive material for an all-solid-state secondary battery, wherein the length of the carbon material is 1 μm to 300 μm. positive current collector; and A positive electrode for an all-solid-state secondary battery comprising: a positive active material layer positioned on the positive current collector and comprising a positive active material, a conductive material for an all-solid-state secondary battery according to any one of claims 1 to 10, and a binder. In Article 11, The above positive active material layer is a positive electrode for an all-solid-state secondary battery that further comprises a sulfide-based solid electrolyte. In Article 12, The above positive active material layer is, based on 100 weight% of the above positive active material layer, The above positive active material is included in an amount of 55% to 99.7% by weight, and The above-mentioned conductive material for a solid-state secondary battery is included in an amount of 0.1% to 5% by weight, and The above binder is included in an amount of 0.1% to 5% by weight, A positive electrode for an all-solid-state secondary battery comprising 0.1% to 35% by weight of the above-mentioned sulfide-based solid electrolyte. In Article 12, The above sulfide-based solid electrolytes are Li2S-P2S5, Li2S-P2S5-LiX (where X is a halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z m S n (m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q A positive electrode for an all-solid-state secondary battery comprising (p, q are integers, and M is P, Si, Ge, B, Al, Ga, or In), or a combination thereof. In Article 12, The above sulfide-based solid electrolyte is a positive electrode for an all-solid-state secondary battery containing an azirodite-type sulfide. In Article 15, The above azirodite-type sulfide is a positive electrode for an all-solid-state secondary battery represented by the following chemical formula 1: [Chemical Formula 1] (Li a M 1 b M 2 c (P) d M 3 e )(S f M 4 g )X h In the above chemical formula 1, 4≤a≤8, and M 1 is Mg, Cu, Ag, or a combination thereof, 0≤b<0.5, and M 2 is Na, K, or a combination thereof, 0≤c<0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, and 0 <d<4, 0≤e<1 이고, M 4 is O, SO n , or a combination thereof, 1.5≤n≤5, 3≤f≤12, 0≤g<2, X is F, Cl, Br, I, or a combination thereof, and 0≤h≤2. In Article 15, The above azirodite-type sulfide is a positive electrode for an all-solid-state secondary battery in the form of particles with an average particle size of 0.1 μm to 3.0 μm. Anode for an all-solid-state secondary battery according to claim 11; cathode; and A solid electrolyte layer located between the anode and the cathode; comprising an all-solid-state secondary battery. In Article 18, The above cathode is a cathode current collector; and All-solid-state secondary battery comprising: a negative electrode coating layer located on the negative electrode current collector and containing a lithium-friendly metal, a carbon material, or a combination thereof. In Article 19, An all-solid-state secondary battery further comprising a lithium metal layer formed by charging between the above-mentioned negative electrode current collector and the above-mentioned negative electrode coating layer.

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