Positive electrode active material for all solid-state battery, and positive electrode and all solid-state battery including same

Abstract

The present invention relates to a positive electrode active material for an all-solid secondary battery, and a positive electrode and an all-solid secondary battery including same. The positive electrode active material for an all-solid secondary battery includes: a core particle containing a lithium transition metal composite oxide; and a coating layer positioned on the surface of the core particle, wherein the coating layer contains an oxygen ion conductive oxide and a lithium metal oxide.

Description

Positive electrode active material for an all-solid-state secondary battery, and a positive electrode and an all-solid-state secondary battery containing the same

[0001] The present invention relates to a cathode active material for an all-solid-state secondary battery, and a cathode and an all-solid-state secondary battery including the same.

[0002] Lithium secondary batteries offer high energy density and are highly portable, making them widely used as power sources for mobile information devices such as smartphones and laptops. Recently, research is actively underway on high-safety, high-capacity lithium secondary batteries for use as power sources for hybrid and electric vehicles, as well as for power storage.

[0003] Commercially available lithium secondary batteries use electrolytes containing flammable organic solvents, posing safety concerns that can lead to explosions or fires in the event of collisions, penetrations, or other problems. Therefore, semi-solid or all-solid-state secondary batteries, which avoid the use of electrolytes, are being proposed. All-solid-state secondary batteries are composed entirely of solid materials, specifically those that utilize solid electrolytes. These all-solid-state secondary batteries are safe, eliminating the risk of electrolyte leakage and explosion, and offer the advantage of being easy to manufacture in thinner forms.

[0004] The cathode for all-solid-state secondary batteries typically contains a cathode active material and a solid electrolyte. The charged cathode active material within the cathode can lose its structural stability as lithium ions escape. When the temperature rises due to repeated charging and discharging, oxygen generated from the cathode active material can cause the battery to catch fire.

[0005] Furthermore, sulfide-based solid electrolytes, which boast excellent lithium ion conductivity, are primarily used as solid electrolytes. Typically, sulfide-based solid electrolytes suffer from irreversible lithium loss at the interface with the cathode active material due to their high reactivity, which drastically reduces long-life characteristics.

[0006] One embodiment is to provide a cathode active material for an all-solid-state secondary battery that can capture oxygen in the form of oxygen ions through an oxygen reduction reaction on the surface of the cathode active material, thereby suppressing oxygen generation even when the temperature rises, while at the same time suppressing the possibility of ignition due to reaction with a solid electrolyte.

[0007] Another embodiment is to provide a cathode and an all-solid-state secondary battery including the cathode active material.

[0008] In one embodiment, a positive electrode active material for an all-solid-state secondary battery is provided, comprising a core particle containing a lithium transition metal composite oxide, a coating layer positioned on the surface of the core particle, and the coating layer comprising an oxygen ion conductive oxide and a lithium-metal-oxide.

[0009] In another embodiment, a positive electrode is provided, comprising: a positive electrode current collector; and a positive electrode active material layer positioned on the positive electrode current collector and including the positive electrode active material described above.

[0010] In another embodiment, an all-solid-state secondary battery is provided, comprising the aforementioned positive electrode, negative electrode, and a solid electrolyte layer positioned between the positive electrode and negative electrode.

[0011] According to an embodiment, a cathode active material for an all-solid-state secondary battery can capture oxygen in the form of oxygen ions through an oxygen reduction reaction on the surface of the cathode active material, thereby suppressing oxygen generation even when the temperature rises, while at the same time suppressing the possibility of ignition due to a reaction with a solid electrolyte.

[0012] The positive electrode and all-solid-state secondary batteries according to other embodiments can exhibit excellent performance by suppressing the reaction between the solid electrolyte and the positive electrode active material, including the positive electrode active material described above.

[0013] Figures 1 and 2 are cross-sectional views schematically showing an all-solid-state secondary battery structure according to one embodiment.

[0014] Figure 3 is a photograph of the positive electrode active material of Example 1 taken using a scanning electron microscope (SEM).

[0015] Figure 4 is a graph showing the Nyquist curves of Example 1 and Comparative Examples 1 and 2.

[0016] Below, specific implementation examples are described in detail so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in various different forms and is not limited to the implementation examples described herein.

[0017] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0018] Here, “combination of these” means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of the components.

[0019] It should be understood that the terms "include," "comprising," or "having" herein are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0020] To clearly illustrate various layers and regions in the drawings, their thicknesses are enlarged, and similar parts are designated by the same drawing reference numerals throughout the specification. When an element such as a layer, film, region, or plate is said to be "over" or "on" another element, this includes not only the case where it is "directly over" the other element, but also the case where there are other elements in between. Conversely, when an element is said to be "directly over" another element, it means that there are no other elements in between.

[0021] Also, here, “layer” includes not only the shape formed on the entire surface when observed in a plan view, but also the shape formed on a portion of the surface.

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

[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] “Metal” is interpreted as a concept that includes common metals, transition metals, and metalloids (semi-metals).

[0025] Cathode active material for all-solid-state secondary batteries

[0026] In an all-solid-state secondary battery, the state of the charged cathode active material—that is, when some or all of the lithium has been removed—can be considered a state in which the structural stability of the cathode active material is relatively compromised. When the temperature rises, oxygen can be generated from the cathode active material. This oxygen can cause ignition in all-solid-state secondary batteries under high-temperature or abnormal conditions.

[0027] The present inventors sought to suppress the possibility of ignition by converting oxygen gas generated from the positive electrode active material into ions, while simultaneously enhancing the interfacial stability between the solid electrolyte and the positive electrode active material, thereby improving fire safety and lifespan characteristics. To this end, the surface of the positive electrode active material for an all-solid-state secondary battery was coated with an oxygen ion-conducting oxide capable of capturing oxygen by converting it into ions, and a lithium metal oxide.

[0028] According to one embodiment, a cathode active material for an all-solid-state secondary battery includes core particles containing a lithium transition metal composite oxide, a coating layer positioned on the surface of the core particles, and the coating layer includes an oxygen ion conductive oxide and a lithium-metal-oxide.

[0029] According to one embodiment, a cathode active material for an all-solid-state secondary battery includes a lithium-metal-oxide as a material for a buffer layer together with an oxygen ion conductive oxide that converts oxygen into oxygen ions and captures them on the surface of core particles, thereby effectively suppressing side reactions at the interface between the cathode active material and the solid electrolyte and deterioration of the solid electrolyte, and suppressing the possibility of ignition due to contact between the sulfide-based solid electrolyte and the cathode active material by converting oxygen gas generated at the cathode into oxygen ions even when the temperature rises after charging.

[0030] core particle

[0031] According to one embodiment, the core particle of the positive electrode active material contains a lithium transition metal composite oxide.

[0032] The above lithium transition metal composite oxide may be used without limitation as long as it is generally used in lithium secondary batteries. For example, the lithium transition metal composite oxide may be a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound), and may include a compound represented by any one of the following chemical formulas.

[0033] Li a A1-b X b D2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5);

[0034] Li a A 1-b X b O 2-c D c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05);

[0035] Li a HAVE BEEN 1-b X b O 2-c D c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05);

[0036] Li a HAVE BEEN 2-b X b O 4-c D c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05);

[0037] Li a Ni 1-b-c Co b X c D α (0.90 ≤ a ≤1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 <α ≤ 2);

[0038] Li a Ni 1-b-c Co b X c O 2-α T α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2);

[0039] Li a Ni 1-b-c Co b X c O 2-α T2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2);

[0040] Li a Ni1-b-c Mr b X c D α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2);

[0041] Li a Ni 1-b-c Mr b X c O 2-α T α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2);

[0042] Li a Ni 1-b-c Mr b X c O 2-α T2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2);

[0043] Li a Ni b HAVE BEEN c G d O2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1);

[0044] Li a Ni b Co c Mr d G e O2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤0.5, 0.001 ≤ e ≤ 0.1);

[0045] Li a NiG b O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1);

[0046] Li a CoG b O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1);

[0047] Li a Mr 1-b Gb O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1);

[0048] Li a Mn2G b O4(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1);

[0049] Li a Mn 1-g G g PO4(0.90 ≤ a ≤ 1.8, 0 ≤ g ≤ 0.5);

[0050] QO2; QS2; LiQS2;

[0051] V2O5; LiV2O5;

[0052] LiZO2;

[0053] LiNiVO4;

[0054] Li (3-f) J2(PO4)3(0 ≤ f ≤ 2);

[0055] Li (3-f) Fe2(PO4)3(0 ≤ f ≤ 2);

[0056] Li a FePO4(0.90 ≤ a ≤ 1.8).

[0057] In the above chemical formulas, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

[0058] The above lithium transition metal composite oxide may be, for example, lithium cobalt composite oxide (LCO), lithium nickel composite oxide (LNO), lithium nickel cobalt composite oxide (NC), lithium nickel cobalt aluminum composite oxide (NCA), lithium nickel cobalt manganese composite oxide (NCM), lithium nickel manganese composite oxide (NM), lithium manganese composite oxide (LMO), or lithium iron phosphate composite oxide (LFP).

[0059] The lithium transition metal composite oxide may be, for example, a lithium nickel-based composite oxide represented by the following chemical formula 1, a lithium cobalt-based composite oxide represented by the following chemical formula 2, a lithium iron phosphate-based composite compound represented by the following chemical formula 3, a cobalt-free lithium nickel-manganese-based composite oxide represented by the following chemical formula 4, or a combination thereof.

[0060] [Chemical Formula 1]

[0061] Li a1 Ni x1 M 1 y1 M 2z1 O 2-b1 X b1

[0062] In the above chemical formula 1, 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 are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0063] In the above chemical formula 1, M 1 and M 2 can be different elements.

[0064] In the above chemical formula 1, 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.

[0065] [Chemical Formula 2]

[0066] Li a2 Co x2 M 3 y2 O 2-b2 X b2

[0067] In the above chemical formula 2, 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 one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is one or more elements selected from the group consisting of F, P and S.

[0068] [Chemical Formula 3]

[0069] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3

[0070] In the above chemical formula 3, 0.9≤a3≤1.8, 0.6≤x3≤1, 0≤y3≤0.4, and 0≤b3≤0.1, and M 4 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is one or more elements selected from the group consisting of F, P and S.

[0071] [Chemical Formula 4]

[0072] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4

[0073] In the above chemical formula 4, 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 one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0074] According to one embodiment, a lithium transition metal composite oxide may be a lithium nickel-based composite oxide represented by the following chemical formula 1.

[0075] The average particle diameter (D) of the above core particles 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. For example, the core particles may have an average particle diameter (D 50 ) with small particles of 1 ㎛ to 9 ㎛ and an average particle diameter (D 50 ) may include a core particle having a particle size range of 10 ㎛ to 25 ㎛. Core particles having such a particle size range can be harmoniously mixed with other components in the positive electrode active material layer and can implement high capacity and high energy density. Here, the average particle size is obtained by selecting 20 or so random particles from a scanning electron microscope image of the core particles, measuring their particle sizes (diameter, or major axis, or major axis length), and then obtaining a particle size distribution, and in the particle size distribution, the diameter (D) of the particles having a cumulative volume of 50% by volume 50 ) may be taken as the average particle diameter.

[0076] The core particle may be in the form of a secondary particle formed by agglomeration of a plurality of primary particles, or may be in the form of a single particle. In addition, the core particle may be spherical or nearly spherical in shape, or may be polyhedral or irregular in shape.

[0077] coating layer

[0078] According to one embodiment, the coating layer is located on the surface of the core particle and includes an oxygen ion conductive oxide and a lithium-metal-oxide.

[0079] Here, the term “oxygen ion conducting oxide” refers to a material that can capture oxygen gas generated when the temperature rises at the positive electrode after battery charging by converting it into oxygen ions. The oxygen ion conducting oxide may be, for example, an incomplete oxide in which a trivalent cation metal atom is substituted for an oxide containing a tetravalent cation metal atom to create a vacancy. Specific examples of such incomplete oxides may include yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), samarium-stabilized zirconia (SmSZ), gadolinium-stabilized zirconia (GdSZ), yttria-doped ceria (YDC), samarium-doped ceria (SmDC), gadolinium-doped ceria (GdDC), delta-bismuth oxide, lanathan gallium oxide, or a combination thereof. The above oxygen ion conductive oxide can suppress the possibility of ignition by removing oxygen gas, which is a raw material for combustion, and at the same time can improve the stability of the interface between the sulfide-based solid electrolyte and the positive electrode active material, thereby improving the performance of the battery, such as safety and life characteristics.

[0080] The lithium-metal-oxide above refers to an oxide containing lithium and a metal other than lithium, and the metal may be one or more elements selected from the group consisting of Al, B, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ta, V, W, Ti, Zn, and Zr. The lithium-metal-oxide is excellent in lowering the interfacial resistance of a lithium-transition metal composite oxide and solid electrolyte particles without affecting the lithium ion resistance in the positive electrode by facilitating the movement of lithium ions.

[0081] The content of the above oxygen ion conductive oxide and lithium metal oxide can be appropriately adjusted as needed.

[0082] The content of the oxygen ion conductive oxide may be greater than 0.1 mol% and less than 5 mol% with respect to 100 mol% of the positive electrode active material including the core particles and the coating layer. For example, the content of the oxygen ion conductive oxide may be 0.14 mol% or more, 0.16 mol% or more, 0.18 mol% or more, 0.2 mol% or more, 0.22 mol% or more, 0.24 mol% or more, 0.26 mol% or more, 0.28 mol% or more, or 0.3 mol% or more, or 4.5 mol% or less, 4 mol% or less, 3.5 mol% or less, 3 mol% or less, 2.5 mol% or less, 2 mol% or less, 1.75 mol% or less, 1.5 mol% or less, 1.25 mol% or less, 1.2 mol% or less, 1.15 mol% or less, 1.1 mol% or less, 1.05 mol% or less, 1 mol% or less, 0.9 mol% or less, 0.8 mol% or less, 0.7 mol% or less, 0.6 mol% Below, it may be 0.5 mol% or less or 0.4 mol% or less. By ensuring the content of the oxygen ion conductive oxide within the above range, the oxygen generated by the temperature increase can be captured as oxygen ions, thereby effectively suppressing the possibility of ignition between the lithium transition metal composite oxide and the solid electrolyte.

[0083] The content of the lithium-metal-oxide may be 0.01 mol% to 5 mol% with respect to 100 mol% of the positive electrode active material including the core particles and the coating layer. For example, the content of the lithium-metal-oxide may be 0.05 mol% or more, 0.1 mol% or more, 0.15 mol% or more, 0.2 mol% or more, 0.25 mol% or more, 0.3 mol% or more, 0.35 mol% or more, 0.4 mol% or more, or 0.44 mol% or more, or 4.5 mol% or less, 4 mol% or less, 3.5 mol% or less, 3 mol% or less, 2.5 mol% or less, 2.25 mol% or less, 2 mol% or less, 1.75 mol% or less, 1.5 mol% or less, 1.25 mol% or less, 1 mol% or less, 0.75 mol% or less, or 0.5 It may be less than 1%.

[0084] Additionally, the content of metal other than lithium in the lithium-metal-oxide may be 0.01 mol% to 5 mol% with respect to 100 mol% of the positive electrode active material including the core particles and the coating layer. For example, the content of metal other than lithium in the lithium-metal-oxide may be 0.05 mol% or more, 0.1 mol% or more, 0.15 mol% or more, 0.2 mol% or more, 0.25 mol% or more, 0.3 mol% or more, 0.35 mol% or more, 0.4 mol% or more, or 0.44 mol% or more, or 4.5 mol% or less, 4 mol% or less, 3.5 mol% or less, 3 mol% or less, 2.5 mol% or less, 2.25 mol% or less, 2 mol% or less, 1.75 mol% or less, 1.5 mol% or less, 1.25 mol% or less, 1 mol% or less, 0.75 mol% or less, or 0.5 mol% or less.

[0085] Even if the content of the lithium-metal-oxide is small, such as within the above range, it is possible to improve the performance of the positive electrode active material by facilitating the movement of lithium ions and electron conduction, while effectively lowering the interfacial resistance between the lithium transition metal composite oxide and the solid electrolyte particles.

[0086] The coating layer may have a single-layer structure in which both an oxygen ion conductive oxide and a lithium-metal oxide are included in one layer; or it may have a double-layer structure in which a first coating layer including an oxygen ion conductive oxide and a second coating layer including a lithium-metal oxide are included.

[0087] When the above coating layer has a single layer structure, the oxygen ion conductive oxide and the lithium metal oxide may be evenly dispersed with each other or may be combined with each other to form a new phase.

[0088] When the coating layer has a double-layer structure, the coating layer includes a first coating layer including a lithium-metal-oxide and a second coating layer including an oxygen ion conductive oxide, and may have a structure in which the first coating layer and the second coating layer are sequentially laminated from the surface of the lithium-transition metal composite oxide, or may have a structure in which the second coating layer and the first coating layer are sequentially laminated from the surface of the lithium-transition metal composite oxide. In one embodiment, the coating layer has a structure in which the first coating layer and the second coating layer are sequentially laminated from the surface of the lithium-transition metal composite oxide, and the second coating layer may be distributed in an island shape on the first coating layer.

[0089] The thickness of the coating layer may be 1 nm to 20 nm. The thickness of the coating layer is assumed to be a single layer, and in the case of a double layer, the first coating layer and the second coating layer may each have a thickness within the aforementioned range. By ensuring the thickness of the coating layer within the aforementioned range, the possibility of ignition between the solid electrolyte and the positive electrode active material when the temperature rises can be effectively suppressed, and the interfacial resistance can be lowered to improve battery performance.

[0090] The shape of the above coating layer may be in the form of a continuous film, or in the form of a discontinuous film, such as an island shape.

[0091] The above coating layer can be formed according to a known method, for example, it can be formed according to a dry coating method or a wet coating method.

[0092] Methods for forming the coating layer including the lithium-metal-oxide include i) a method of dry mixing and coating lithium-metal-oxide powder, ii) a method of dry mixing and then heat treating to coat, iii) a method of dry mixing and then heat treating to coat a lithium raw material such as LiOH or Li2CO3 and a metal oxide, iv) a wet method of adding an active material to a solvent in which a lithium precursor and a metal precursor are dissolved, boiling the active material, and then heat treating the mixture, v) a wet method similar to iv) but coating by spray drying, vi) a method of spraying the solvent of iv) onto a dispersed active material and then coating, vii) atomic layer decomposition (ALD), etc. As long as it is a method for forming the coating layer including the lithium-metal-oxide, it is not limited to the exemplified methods.

[0093] As a method for forming a coating layer including the oxygen ion conductive oxide, there are also provided i) a method of dry mixing and coating powder of the oxygen ion conductive oxide, ii) a method of dry mixing and then heat treating to coat, iii) a method of mixing a heterogeneous metal oxide included in the oxygen ion conductive oxide (when the oxygen ion conductive oxide is yttria-stabilized zirconia, the heterogeneous metal oxide may be, for example, Y2O3 or ZrO2) and then heat treating to coat, iv) a wet method of adding an active material to a solvent in which a heterogeneous metal precursor is dissolved, boiling it, and then heat treating, v) a wet method similar to iv) but coating by spray drying, vi) a method of spraying the solvent of iv) onto a dispersed active material and coating, vii) atomic layer decomposition (ALD), etc. As long as it is a method for forming a coating layer including the oxygen ion conductive oxide, it is not limited to the exemplified methods.

[0094] According to one embodiment, the first coating layer comprising a lithium-metal-oxide may be formed by a method of dry mixing a lithium raw material and a metal oxide among the methods listed above, followed by heat treatment and coating. The lithium raw material and the metal oxide may be dry mixed at a molar ratio of 1:1 to 10:1, and the heat treatment temperature may be performed at 300°C to 1000°C for 5 to 20 hours.

[0095] The second coating layer comprising an oxygen ion conductive oxide according to one embodiment may be formed by a method of dry mixing and coating a powder of an oxygen ion conductive oxide among the methods listed above. The specific type of the oxygen ion conductive oxide is as described above.

[0096]

[0097] anode

[0098] According to one embodiment, a cathode includes a cathode current collector; and a cathode active material layer positioned on the cathode current collector and including the cathode active material described above.

[0099] positive current collector

[0100] The positive electrode current collector may include, but is not limited to, aluminum, nickel, stainless steel, or a combination thereof. The thickness of the positive electrode current collector is not particularly limited and may be, for example, 1 μm to 30 μm, 1 μm to 20 μm, or 1 μm to 10 μm.

[0101] positive electrode active material layer

[0102] The above positive electrode active material layer includes the above-described positive electrode active material.

[0103] Since the above positive electrode active material is as described above, it is omitted below.

[0104] The content of the positive electrode active material may be 55 wt% to 99 wt% with respect to 100 wt% of the positive electrode active material layer, for example, 55 wt% to 90 wt%, or 55 wt% to 85 wt%.

[0105] The above positive electrode active material layer may include a solid electrolyte, and the solid electrolyte may include at least one of an organic solid electrolyte, an inorganic solid electrolyte, and a hybrid composite solid electrolyte.

[0106] The above organic solid electrolyte may be a polymer solid electrolyte in which dissolved lithium and a polymer material are mixed. The above inorganic solid electrolyte may be an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halide-based solid electrolyte, or a combination thereof. The above hybrid composite solid electrolyte is a solid electrolyte that combines the advantages of organic solid electrolyte and inorganic solid electrolyte and eliminates the disadvantages, and adds inorganic particles to an organic matrix, and the organic matrix is ​​PVdF (polyvinylidene fluoride), PVdF-HFP copolymer (polyvinylidene fluoride-hexafluoropropylene copolymer), PVdF-TFE copolymer (polyvinylidene fluoride-tetrafluoroethylene), PVdF-CTFE copolymer (polyvinylidene fluoride-chlorotrifluoroethylene), PVdF-PFA copolymer (polyvinylidene fluoride-perfluorovinylether), PAN (polyacrylonitrile), PMMA (poly(methyl methacrylate)), PEO (poly(ethylene oxide)), PPO (polypropylene oxide), PVC (polyvinyl chloride), PVA (polyvinyl alcohol), PVAc (polyvinyl acetate), PVN (poly vinylnaphthalene), polyester sulfide (polyester The inorganic particles may include at least one selected from oxide-based, sulfide-based, phosphate-based, and LiPON-based inorganic materials having lithium ion conductivity.

[0107] A solid electrolyte according to one embodiment may include an inorganic solid electrolyte, and specifically, may include a sulfide-based solid electrolyte.

[0108] Sulfide-based solid electrolytes can achieve high ionic conductivity, but they are easily degraded by moisture and air, and may cause side reactions at the interface with the positive electrode active material or accelerated deterioration at the interface. However, when a positive electrode active material according to one embodiment is mixed with a sulfide-based solid electrolyte and applied to the positive electrode, the interfacial stability of the positive electrode active material and the sulfide-based solid electrolyte is significantly improved, thereby improving performance such as the lifespan characteristics of the all-solid-state secondary battery. Furthermore, since oxygen gas generation is suppressed, the fire safety of the all-solid-state secondary battery can be further improved.

[0109] The above sulfide-based solid electrolyte is, for example, Li2S-P2S5, Li2S-P2S5-LiX (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, n are integers, 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 a combination thereof.

[0110] 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 them. Within the above mixing ratio range, a sulfide-based solid electrolyte having excellent ionic conductivity can be produced. Here, the ionic conductivity can be further improved by further including other components such as SiS2, GeS2, and B2S3.

[0111] Methods for mixing sulfur-containing raw materials for producing sulfide-based solid electrolytes include mechanical milling or the solution method. Mechanical milling involves placing raw materials in a ball mill reactor and vigorously stirring them to finely atomize and mix them. Using the solution method, the raw materials are mixed in a solvent to obtain a solid electrolyte as a precipitate. Furthermore, heat treatment after mixing can solidify the crystals of the solid electrolyte and improve ionic conductivity. For example, a sulfide-based solid electrolyte can be produced by mixing sulfur-containing raw materials and heat-treating them twice or more, resulting in a sulfide-based solid electrolyte with high ionic conductivity and robustness.

[0112] According to one embodiment, a sulfide-based solid electrolyte can be manufactured through, for example, a first heat treatment in which sulfur-containing raw materials are mixed and calcined at 120°C to 350°C, and a second heat treatment in which the first heat treatment result is mixed and calcined at 350°C to 800°C. The first heat treatment and the second heat treatment can each be performed 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. The first heat treatment can have the effect of milling small raw materials, and the second heat treatment can synthesize the final solid electrolyte. Through two or more such heat treatments, a high-performance sulfide-based solid electrolyte with high ionic conductivity and robustness can be obtained, and such a solid electrolyte can be said to be 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.

[0113] For example, the sulfide-based solid electrolyte may include an argyrodite-type sulfide. The argyrodite-type sulfide may be, for example, Li a M b P c S d A e (wherein a, b, c, d, and e are all 0 or more and 12 or less, M is Ge, Sn, Si, or a combination thereof, and A is F, Cl, Br, or I) and can be expressed by the chemical formula, and a specific example is Li 7-x PS 6-x A x (x is 0.2 or more and 1.8 or less, and A is F, Cl, Br, or I) can be expressed by the chemical formula. The above argyrodite-type sulfide is specifically Li3PS4, Li7P3S 11 , Li7PS6, Li6PS5Cl, Li6PS5Br, Li 5.8 PS4.8 Cl 1.2 , Li 6.2 PS 5.2 Br 0.8 It could be the back.

[0114] Sulfide-based solid electrolytes containing these argyrodite-type sulfides have an ionic conductivity of 10 that of typical liquid electrolytes at room temperature. -4 10 inland -2 It has a high ionic conductivity approaching the S / cm range, can form a close bond between a positive electrode active material and a solid electrolyte without causing a decrease in ionic conductivity, and further can form a close interface between an electrode layer and a solid electrolyte layer. An all-solid-state secondary battery including this can have improved battery performance, such as rate characteristics, Coulombic efficiency, and cycle life characteristics.

[0115] The argyrodite-type sulfide-based solid electrolyte may include, for example, a compound represented by the chemical formula 5 below.

[0116] [Chemical Formula 5]

[0117] (Li a M 1 b M 2 c )(P d M 3 e )(S f M 4 g )X h

[0118] In the above chemical formula 5, 4≤a≤8, and M 1 is Mg, Ca, Cu, Ag, or a combination thereof, and 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 N,O,SO n, or a combination thereof, and 1.5≤n≤5, 3≤f≤12, 0≤g<2, and X is F, Cl, Br, I, or a combination thereof, and 0≤h≤2.

[0119] For example, in chemical formula 5, a halide element (X) may be included as an essential element, in which case 0 <h≤2로 표시될 수 있다. 일 예로 화학식 5에 M 1 Elements may be required, in which case 0 <b<0.5로 표시될 수 있다. 화학식 5에서 M 3 can be understood as an element substituted in place of P and 0 <e<1일 수 있다. 화학식 5에서 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 Go SO n If SO n It can be, for example, S4O6, S3O6, S2O3, S2O4, S2O5, S2O6, S2O7, S2O8, SO4, or SO5, and can be, for example, SO4.

[0120] For example, in chemical formula 5, a+b+c+h=7, d+e=1, and f+g+h=6.

[0121] As a specific example, argyrodite-type sulfide-based solid electrolytes 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 Cu0.06 )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 combinations thereof, but are not limited thereto.

[0122] An argyrodite-type sulfide-based solid electrolyte can be manufactured, for example, by mixing lithium sulfide and phosphorus sulfide, and optionally, lithium halide. After mixing these, a heat treatment may be performed. The heat treatment may include, for example, two or more heat treatment steps. Here, manufacturing an argyrodite-type sulfide-based solid electrolyte may include, for example, a first heat treatment of mixing raw materials and calcining at 120°C to 350°C, and a second heat treatment of mixing the resultant of the first heat treatment again and calcining at 350°C to 800°C.

[0123] The above sulfide-based solid electrolyte may be in the form of particles, and the average particle diameter (D) of the particles 50) may be 5.0 ㎛ or less, for example, 0.1 ㎛ to 5.0 ㎛, 0.5 ㎛ to 5.0 ㎛, 0.5 ㎛ to 4.0 ㎛, 0.5 ㎛ to 3.0 ㎛, 0.5 ㎛ to 2.0 ㎛, or 0.5 ㎛ to 1.0 ㎛. The solid electrolyte may be small particles of 0.1 ㎛ to 1.9 ㎛, large particles of 2.0 ㎛ to 5.0 ㎛, or a mixture thereof. The average particle diameter of the sulfide-based solid electrolyte particles may be measured by an electron microscope image, and for example, a particle size distribution is obtained by measuring the size (diameter or major axis length) of about 20 particles in a scanning electron microscope image, where D 50 It may have been calculated.

[0124] The content of the sulfide-based solid electrolyte may be 0.1 wt% to 50 wt% with respect to 100 wt% of the positive electrode active material layer, for example, 1 wt% to 40 wt%, or 5 wt% to 40 wt%, 8 wt% to 40 wt%, or 10 wt% to 40 wt%.

[0125] The above positive electrode active material layer may optionally further include a binder, a conductive material, or a combination thereof.

[0126] The binder serves to adhere the positive electrode active material particles well to each other and also to adhere the positive electrode active material well to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc. In the positive electrode active material layer, the content of the binder may be approximately 0.1 wt% to 5 wt% based on 100 wt% of the positive electrode active material layer.

[0127] The conductive material is used to provide conductivity to the electrode, and any material that does not cause chemical changes and is electronically conductive can be used in the battery. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials containing copper, nickel, aluminum, silver, etc. and in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof. The content of the conductive material in the positive electrode active material layer may be 0 wt% to 3 wt%, 0.01 wt% to 2 wt%, or 0.1 wt% to 1 wt% based on 100 wt% of the positive electrode active material layer.

[0128] All-solid-state secondary battery

[0129] In one embodiment, an all-solid-state secondary battery is provided, including the aforementioned positive electrode, negative electrode, and a solid electrolyte layer positioned between the positive electrode and negative electrode.

[0130] Fig. 1 is a cross-sectional view of an all-solid-state secondary battery according to an embodiment. Referring to Fig. 1, the all-solid-state secondary battery (100) has a structure in which an electrode assembly in which 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) are laminated is housed in a battery case. 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 an assembly in which two unit cells including a cathode (400), a solid electrolyte layer (300), and an anode (200) are laminated, but three or more may be laminated, for example, 2 to 100, 3 to 50, 4 to 20, etc.

[0131] cathode

[0132] An anode for an all-solid-state secondary battery includes a cathode current collector and a cathode active material layer positioned on the cathode current collector. The cathode active material layer includes a cathode active material and may optionally further include a binder, a conductive material, or a combination thereof.

[0133] The above 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.

[0134] The material capable of reversibly intercalating / deintercalating the lithium ions may include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0135] As the above lithium metal alloy, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0136] As the material capable of doping and dedoping the lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used, and the Si-based negative electrode active material may be silicon, a silicon-carbon composite, or SiO. x (0 < x < 2), Si-Q alloy (wherein Q is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn-based negative electrode active materials include Sn, SnO2, Sn-R alloy (wherein R is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), and at least one of these may be mixed with SiO2 for use. The above elements Q and R may be selected from the group consisting of 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, and combinations thereof.

[0137] For example, the negative active material may include silicon-carbon composite particles. The average particle diameter (D) of the silicon-carbon composite particles 50 ) may be, for example, 0.5 ㎛ to 20 ㎛. The average particle diameter (D50 ) is measured by a particle size analyzer and means the diameter of particles having a cumulative volume of 50% by volume in the particle size distribution. 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 including silicon particles, and a carbon coating layer located on the surface of the core. The average particle diameter (D) of the silicon particles in the core 50 ) may be 10 nm to 1 ㎛, 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 nm 내지 100 nm일 수 있다.

[0138] For example, the silicon-carbon composite particle may include a core including silicon particles and crystalline carbon, and a carbon coating layer located on the surface of the core and including amorphous carbon. For example, in the silicon-carbon composite particle, the amorphous carbon may not be present in the core but may be present 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 pitch, mesophase pitch, petroleum pitch, coal oil, petroleum heavy oil, or a polymer resin (phenol resin, furan resin, polyimide resin, etc.). At this time, the content of the crystalline carbon may be 10 wt% to 70 wt%, and the content of the amorphous carbon may be 20 wt% to 40 wt% with respect to 100 wt% of the silicon-carbon composite particle.

[0139] In the above silicon-carbon composite particle, 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.

[0140] The silicon-carbon composite particles described above can effectively suppress problems such as volume expansion, structural collapse, or particle crushing due to charge and discharge, thereby preventing the phenomenon of conductive path disconnection, realizing high capacity and high efficiency, and are advantageous for use under high voltage or fast charging conditions.

[0141] The above Si-based negative electrode active material or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material. When the Si-based negative electrode active material or Sn-based negative electrode active material and the carbon-based negative electrode active material are used in combination, the mixing ratio can be 1:99 to 90:10 by weight.

[0142] The content of the negative active material in the above negative active material layer may be 95 wt% to 99 wt% with respect to 100 wt% of the negative active material layer.

[0143] In one embodiment, the negative electrode active material layer further includes a binder and may optionally further include a conductive material. The content of the binder in the negative electrode active material layer may be 1 wt% to 5 wt% based on 100 wt% of the negative electrode active material layer. In addition, when the negative electrode active material layer further includes a conductive material, the negative electrode active material layer may include 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material.

[0144] The above binder serves to adhere the negative electrode active material particles well to each other and also to adhere the negative electrode active material well to the current collector. The binder may be an insoluble binder, a water-soluble binder, or a combination thereof.

[0145] The above-mentioned non-aqueous binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, an ethylene propylene copolymer, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0146] The water-soluble binder may be a rubber-based binder or a polymer resin binder. 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, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0147] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity as a type of thickener may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li. The amount of the thickener used may be 0.1 to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0148] The above conductive material is used to provide conductivity to the electrode, and in the battery to be formed, any material that does not cause a chemical change and is electronically conductive can be used. Examples of conductive materials that can be used include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials including copper, nickel, aluminum, silver, etc. and in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or conductive materials including mixtures thereof.

[0149] The negative electrode current collector may be 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.

[0150] As another example, the negative electrode for an all-solid-state secondary battery may be a precipitation-type negative electrode. The precipitation-type negative electrode may refer to a negative electrode that does not include a negative electrode active material when the battery is assembled, but in which lithium metal or the like is precipitated or deposited on the negative electrode when the battery is charged, and this acts as a negative electrode active material.

[0151] 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 current collector (401) and a negative electrode coating layer (405) positioned on the current collector. An all-solid-state secondary battery including such a precipitation-type negative electrode (400') starts initial charging in a state in which no negative electrode active material is present, and during charging, high-density lithium metal is precipitated or deposited between the 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 may function as a negative electrode active material. Accordingly, in an all-solid-state secondary battery that has been charged more than once, the precipitation-type negative electrode (400') may include, for example, a current collector (401), a lithium metal layer (404) positioned on the current collector, and a negative electrode coating layer (405) positioned on the metal layer. The lithium metal layer (404) refers to a layer in which lithium metal or the like is precipitated during the charging process of the battery, and may be referred to as a metal layer, a lithium layer, a lithium deposition layer, or a negative electrode active material layer.

[0152] The above cathode coating layer (405) may be referred to as a lithium electrodeposition induction layer or a cathode catalyst layer, and may include a metal, carbon material, or a combination thereof that acts as a catalyst.

[0153] The metal may be a lithium-philic 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 is present in the form of particles, the average particle diameter (D 50 ) may be less than about 4 μm, for example, 10 nm to 4 μm.

[0154] The carbon material may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The crystalline carbon may be, for example, natural graphite, artificial graphite, mesophase carbon microbeads, or a combination thereof. The amorphous carbon may be, for example, carbon black, activated carbon, acetylene black, Denka black, Ketjen black, or a combination thereof.

[0155] When the above-described 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 above-described negative electrode coating layer (405) may include, for example, a carbon material supported with a catalytic metal, or may include a mixture of metal particles and carbon material particles.

[0156] The above-described cathode coating layer (405) may include, for example, the above-described lithium-philic metal and amorphous carbon, in which case the precipitation of the lithium metal may be effectively promoted. As a specific example, the cathode coating layer (405) may include a composite in which a lithium-philic metal is supported on amorphous carbon.

[0157] The above cathode coating layer (405) may further include a binder, and the binder may be, for example, a conductive binder. In addition, the above cathode coating layer (405) may further include general additives such as fillers, dispersants, and ionic conductive agents.

[0158] The thickness of the cathode coating layer (405) may be, for example, 100 nm to 20 ㎛, or 500 nm to 10 ㎛, or 1 ㎛ to 5 ㎛.

[0159] The above-described precipitated negative electrode (400') may further include, for example, a thin film on the surface of the current collector, i.e., between the current collector and the negative electrode 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 type thereof or may be composed of multiple types of alloys. The thin film may further flatten the precipitated form 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, a vacuum deposition method, a sputtering method, a plating method, etc. The thickness of the thin film may be, for example, 1 nm to 500 nm.

[0160] 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.

[0161] 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 may be difficult to perform the role of a lithium storage, and if it is too thick, the battery volume may increase and performance may deteriorate.

[0162] When such a precipitation-type cathode is applied, the cathode coating layer (405) can play a role in protecting the lithium metal layer (404) and suppressing the precipitation growth of lithium deadlight. Accordingly, short-circuiting and capacity reduction of the all-solid-state secondary battery can be suppressed, and the lifespan characteristics can be improved.

[0163] solid electrolyte layer

[0164] In an all-solid-state secondary battery according to one embodiment, the solid electrolyte layer (300) may include an inorganic solid electrolyte such as a sulfide-based solid electrolyte or an oxide-based solid electrolyte.

[0165] Since the sulfide-based solid electrolyte has been described above, a detailed description will be omitted.

[0166] Oxide-based inorganic solid electrolytes include, 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 mixtures thereof.

[0167] Meanwhile, the average particle diameter (D) of the solid electrolyte included in the solid electrolyte layer (300) 50 ) is the average particle diameter (D) of the solid electrolyte contained in the positive electrode (200). 50 ) may be larger than the average particle size of the solid electrolyte (200). In this case, the 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 ㎛ to 1.9 ㎛, or 0.1 ㎛ to 1.0 ㎛, and the average particle diameter (D) of the solid electrolyte included in the solid electrolyte layer (300) 50 ) may be 2.0 ㎛ to 5.0 ㎛, or 2.0 ㎛ to 4.0 ㎛, or 2.5 ㎛ to 3.5 ㎛. When this particle size range is satisfied, the energy density of the all-solid-state secondary battery can be maximized while the transfer of lithium ions is facilitated, thereby suppressing resistance and thus improving the overall performance of the all-solid-state secondary battery.

[0168] The solid electrolyte layer (300) may further include a binder in addition to the solid electrolyte. The binder may include, for example, nitrile-butadiene rubber, hydrogenated nitrile-butadiene rubber, styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluoroelastomer, polydimethylsiloxane, polyethylene oxide, polyvinylpyrrolidone, polyvinylpyridine, chlorosulfonated polyethylene, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene, polypropylene, ethylene propylene copolymer, ethylene propylene diene copolymer, polyamideimide, polyimide, poly(meth)acrylate, polyacrylonitrile, polystyrene, polyurethane, or a combination thereof.

[0169] The solid electrolyte layer (300) can be formed by adding a solid electrolyte to a binder solution, coating the same on a base film, and drying the same. The solvent of the binder solution may be isobutyryl isobutyrate, xylene, toluene, benzene, hexane, or a combination thereof. Since the solid electrolyte layer formation process is widely known in the art, a detailed description thereof will be omitted.

[0170] The solid electrolyte layer (300) may further include an alkali metal salt, and / or an ionic liquid, and / or a conductive polymer.

[0171] The above 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 may improve ion conductivity by enhancing the lithium ion mobility of the solid electrolyte layer.

[0172] The above lithium salts include, for example, LiSCN, LiN(CN)2, Li(CF3SO2)3C, LiC4F9SO3, LiN(SO2CF2CF3)2, LiCl, LiF, LiBr, LiI, LiB(C2O4)2, LiBF4, LiBF3(C2F5), lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LIODFB), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(trifluoro methanesulfonyl)imide (LiTFSI, LiN(SO2CF3)2), lithium bis(fluorosulfonyl)imide (LiFSI, It may include LiN(SO2F)2), LiCF3SO3, LiAsF6, LiSbF6, LiClO4 or mixtures thereof.

[0173] In addition, the lithium salt may be an imide-based one, and for example, the imide-based lithium salt may include lithium bis(trifluoro methanesulfonyl)imide (LiTFSI, LiN(SO2CF3)2), lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO2F)2). The lithium salt may maintain or improve ionic conductivity by appropriately maintaining chemical reactivity with an ionic liquid.

[0174] The above ionic liquid has a melting point below room temperature and is a salt or room-temperature molten salt that is liquid at room temperature and consists only of ions.

[0175] The above 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.

[0176] The ionic liquid may be at least one 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-methylimidazolium bis(trifluoromethylsulfonyl)amide, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide.

[0177] In the above solid electrolyte layer, the weight ratio of the solid electrolyte and the ionic liquid may be 0.1:99.9 to 90:10, 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 improving 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.

[0178] The above-mentioned all-solid-state secondary battery may be a unit cell having a structure of positive electrode / solid electrolyte layer / negative electrode, a bi-cell having a structure of negative electrode / solid electrolyte layer / positive electrode / solid electrolyte layer / negative electrode, or a laminated battery in which the structure of the unit cell is repeated.

[0179] The shape of the above-mentioned all-solid-state secondary battery is not particularly limited, and may be, for example, coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flat, etc. In addition, the above-mentioned all-solid-state secondary battery can be applied to large-scale batteries used in electric vehicles, etc. For example, the above-mentioned 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, and for example, it can be used in electric bicycles or power tools, etc. In addition, the above-mentioned all-solid-state secondary battery can be used in various fields such as portable electronic devices.

[0180] Hereinafter, examples and comparative examples of the present invention will be described. However, the examples described below are merely examples of the present invention, and the present invention is not limited to the examples described below.

[0181] Example 1

[0182] (1) Manufacturing of positive electrode active material

[0183] LiNi as a lithium transition metal composite oxide 0.945 Co 0.04 Al 0.015 O2 was prepared, and the lithium-transition metal composite oxide was introduced into a Henschel mixer, and 1.05 mol% of anhydrous lithium hydroxide (LiOH) and 0.35 mol% of zirconia (ZrO2) as raw materials for forming a lithium-metal-oxide coating layer were introduced and mixed. Then, by heat treatment at 500°C for 15 hours under O2 conditions, a first coating layer including lithium-metal-oxide was formed on the surface of the core particle containing the lithium-transition metal composite oxide. Then, 0.3 mol% of yttria-stabilized zirconia (YSZ) as a raw material for forming a coating layer including an oxygen ion conductive oxide was introduced into the Henschel mixer and mixed, thereby manufacturing a cathode active material in which a first coating layer including lithium-metal-oxide and a second coating layer including oxygen ion conductive oxide were sequentially formed on the surface of the core particle containing the lithium-transition metal composite oxide.

[0184] A photograph of the manufactured positive electrode active material taken with a scanning electron microscope (SEM) is shown in Fig. 3. In Fig. 3, it can be seen that the first coating layer and the second coating layer are sequentially laminated, and the second coating layer is distributed in a sea-like manner on the first coating layer.

[0185] (2) Manufacturing of bipolar mixture

[0186] As the positive electrode active material and sulfide-based solid electrolyte, an argyrodite-type solid electrolyte (Li6PS5Cl, D 50 =0.8㎛) and carbon nanofibers as a conductive material were mixed in a weight ratio of 60:35:5 to manufacture a cathode mixture.

[0187] (3) Manufacturing of all-solid-state secondary batteries

[0188] A stainless steel block was placed in a mold with an inner diameter of 13Φ and made of polyether ether ketone (PEEK) for insulation, and a 20㎛ lithium metal foil was placed on the block to serve as a cathode. On the prepared cathode, an argyrodite-type solid electrolyte (Li6PS5Cl, D 50 =3.0㎛) was added and 150 mg of the cathode composite manufactured through the above process was applied under uniaxial pressure (0.1 ton) to form an electrolyte membrane. On top of the electrolyte membrane, 15 mg of the cathode composite manufactured through the above process was added, a stainless steel block was added, and 1-axis pressure (4 ton) was applied for 2 minutes to form a cathode, and an all-solid-state secondary battery was manufactured.

[0189]

[0190] Comparative Example 1

[0191] A cathode active material, cathode mixture, and all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that neither lithium-metal-oxide nor oxygen ion conductive oxide was added during the manufacture of the cathode active material of Example 1.

[0192]

[0193] Comparative Example 2

[0194] A cathode active material, cathode mixture, and all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that only lithium-metal-oxide was added and no oxygen ion conductive oxide was added when manufacturing the cathode active material of Example 1.

[0195]

[0196] Evaluation Example 1: Interface Resistance Evaluation

[0197] For the all-solid-state secondary batteries manufactured according to Example 1 and Comparative Examples 1 and 2, the impedance was measured over an amplitude of ±10 mV and a frequency range of 10 mHz to 1 MHz using an impedance analyzer (Zive MP1 potentiostat / galvanostat / impedance analyzer), and the impedance was expressed as a Nyquist plot expressed on a complex plane. The all-solid-state secondary batteries manufactured according to Example 1 and Comparative Examples 1 and 2 were charged at 4.25 V CC / CV conditions at 45°C and 0.1 C-rate to a SOC (State of Charge) of 100, and after cut-off at a current of 0.05 C rate, a stabilization time of 1 hour was allowed, and the measurement was made in a fully charged state. The interfacial resistance of the battery is determined by the position and size of the semicircle.

[0198] Figure 4 is a Nyquist diagram of Example 1 and Comparative Examples 1 and 2.

[0199]

[0200] Evaluation Example 2: Performance Evaluation of All-Solid-State Secondary Battery

[0201] The all-solid-state secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 4 were charged to an upper limit voltage of 4.25 V under constant current / constant voltage (CC / CV) conditions of 0.1 C at 45°C, then cut-off at a current of 0.05 C rate while maintaining the constant voltage, and then discharged at 0.1 C to a final voltage of 2.5 V to perform initial charge / discharge, and the initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency are shown in Table 1 below.

[0202] Initial Charge / Discharge Initial Charge Capacity (mAh / g) Initial Discharge Capacity (mAh / g) Initial Efficiency (%) Example 1237.4202.485.3 Comparative Example 1227.4184.381.2 Comparative Example 2238.4205.286.1

[0203]

[0204] Evaluation Example 3: Fever Safety Evaluation

[0205] The all-solid-state secondary batteries manufactured in Example 1 and Comparative Examples 1 and 2 were charged to 100% SOC, and the batteries were disassembled to collect only the positive electrode portion to perform differential scanning calorimetry (DSC) analysis. The DSC analysis was performed using a high-pressure cell composed of a stainless steel capsule and a gold gasket in a N2 atmosphere at a heating rate of 5°C per minute in the range of 40 to 500°C, and the endothermic-exothermic peaks occurring in the range of 150 to 250°C were compared, and the exothermic reaction that occurs when oxygen is generated from the positive electrode active material charged in that range and the oxygen reacts with the material in the positive electrode can be confirmed.

[0206] Peak start temperature (℃) Total calorific value (J / g) Example 1 199.37 2 15.4 Comparative Example 1 183.5 2 4 18.2 Comparative Example 2 188.27 2 7 7.6

[0207] Referring to Table 2 above, Example 1 had a higher peak start temperature and a lower total calorific value compared to Comparative Examples 1 and 2, indicating that the exothermic reaction was suppressed by the oxygen ion conductor added to Example 1, thereby improving the exothermic safety. [Explanation of symbols]

[0208] 100: All-solid-state secondary battery 200: Cathode

[0209] 201: Cathode current collector 203: Cathode active material layer

[0210] 300: solid electrolyte layer 400: cathode

[0211] 401: Negative current collector 403: Negative active material layer

[0212] 400': Precipitation type cathode 404: Lithium metal layer

[0213] 405: Cathode coating layer 500: Elastic layer

Claims

1. Core particles containing a lithium transition metal composite oxide, and Comprising a coating layer located on the surface of the core particle, The above coating layer is a positive electrode active material for an all-solid-state secondary battery, comprising an oxygen ion conductive oxide and a lithium metal oxide.

2. In paragraph 1, The above lithium transition metal composite oxide is a lithium nickel-based composite oxide represented by the following chemical formula 1, a positive electrode active material for an all-solid-state secondary battery: [Chemical Formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In the above chemical formula 1, 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 are each independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

3. In paragraph 2, A positive electrode active material for an all-solid-state secondary battery, wherein 0.8≤x1≤1, 0≤y1≤0.2, and 0≤z1≤0.2 in the above chemical formula 1.

4. In paragraph 1, The above oxygen ion conductive oxide is yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), samarium-stabilized zirconia (SmSZ), gadolinium-stabilized zirconia (GdSZ), yttria-doped ceria (YDC), samarium-doped ceria (SmDC), gadolinium-doped ceria (GdDC), delta-bismuth oxide, lanathan gallium oxide, or a combination thereof, a cathode active material for an all-solid-state secondary battery.

5. In paragraph 1, A cathode active material for an all-solid-state secondary battery, wherein the metal of the lithium-metal-oxide is at least one element selected from the group consisting of Al, B, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ta, V, W, Ti, Zn, and Zr.

6. In paragraph 1, A positive electrode active material for an all-solid-state secondary battery, wherein the content of the oxygen ion conductive oxide is greater than 0.1 mol% and less than 5 mol% with respect to 100 mol% of the positive electrode active material.

7. In paragraph 1, A positive electrode active material for an all-solid-state secondary battery, wherein the content of the lithium-metal-oxide is 0.01 mol% to 5 mol% with respect to 100 mol% of the positive electrode active material.

8. In paragraph 1, A positive electrode active material for an all-solid-state secondary battery, wherein the content of a metal other than lithium in the lithium-metal-oxide is 0.01 mol% to 5 mol% with respect to 100 mol% of the positive electrode active material.

9. In paragraph 1, A positive electrode active material for an all-solid-state secondary battery, wherein the coating layer has a single-layer structure in which both an oxygen ion conductive oxide and a lithium-metal oxide are included in one layer; or a double-layer structure in which a first coating layer including an oxygen ion conductive oxide and a second coating layer including a lithium-metal oxide are included.

10. In paragraph 9, The coating layer has a double layer structure including a first coating layer including the oxygen ion conductive oxide and a second coating layer including the lithium-metal-oxide, A positive electrode active material for an all-solid-state secondary battery, wherein the second coating layer is distributed in an island shape on the first coating layer.

11. In paragraph 1, A positive electrode active material for an all-solid-state secondary battery, wherein the thickness of the coating layer is 1 nm to 20 nm.

12. In paragraph 1, A positive electrode active material for an all-solid-state secondary battery, wherein the shape of the above coating layer is formed in the form of a continuous film or in the form of a discontinuous film such as an island shape.

13. A positive electrode for an all-solid-state secondary battery, comprising a positive electrode current collector and a positive electrode active material layer positioned on the positive electrode current collector and including the positive electrode active material of any one of claims 1 to 12.

14. In paragraph 13, A positive electrode for an all-solid-state secondary battery, wherein the positive electrode active material layer further comprises an inorganic solid electrolyte.

15. In paragraph 14, The above inorganic solid electrolyte is a sulfide-based solid electrolyte, and is a positive electrode for an all-solid-state secondary battery.

16. An all-solid-state secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer positioned between the positive electrode and the negative electrode of clause 13.

17. In paragraph 16, An all-solid-state secondary battery, wherein the solid electrolyte layer comprises a sulfide-based solid electrolyte.

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